book of abstracts - campodeano.com of... · flowing matter 2016 book of abstracts 11th-15th january...

Flowing Matter 2016

Book of Abstracts

11th-15th January 2016

Porto, Portugal

Edited by Laura Campo-DeañoPorto, 2016

Contents

1 Introduction 1

2 Invited Talks 3

Mechanical Yield to Plastic Flow in Amorphous Materials . . . . . . . . . . . . . . . 4

Turbulence modeling for polymer solutions . . . . . . . . . . . . . . . . . . . . . . . . 5

Diffusive and convective surface (nano)droplets . . . . . . . . . . . . . . . . . . . . . 6

Bio-inspired sensing of complex flows . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Rheology of dense suspensions of non colloidal spheres in Newtonian and yield-stressfluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Hydrodynamics and phase behaviour of biologically active suspensions . . . . . . . . 10

Microorganisms in flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

A scalable platform for functional nanomaterials . . . . . . . . . . . . . . . . . . . . . 12

How elastic instabilities in the flow of entangled polymer solutions explain an unex-pected increase in oil recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Single and collective fiber dynamics in microflows . . . . . . . . . . . . . . . . . . . . 17

3 Other Contributions 19

Earthquake statistics inferred from plastic events in soft-glassy materials . . . . . . . 20

Phase and precession evolution in the Burgers equation . . . . . . . . . . . . . . . . . 21

Clustering and Turbophoresis in a Shear Flow without Walls . . . . . . . . . . . . . . 22

Confinement and Clustering of Floaters in Stratified Turbulence . . . . . . . . . . . . 23

Relaxation dynamics of functionalized colloids on attractive substrates . . . . . . . . 24

Lagrangian analysis of rotating Rayleigh-Bénard turbulence . . . . . . . . . . . . . . 25

Effects of viscoelasticity on droplet dynamics and break-up in microfluidic T-Junctions: a Lattice Boltzmann study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Local synchronization of inertial beads in a ionic time-dependent chaotic flow . . . . . 27

I

CONTENTS

Modelling of Residence Time Dispersion of Falling Droplets . . . . . . . . . . . . . . 28

Measurements of diffusion in anisotropic fluids . . . . . . . . . . . . . . . . . . . . . . 29

Manipulating surface plasmons in graphene ribbons with liquid crystal . . . . . . . . 30

Entropic electrokinetics: How to use geometrical constraints to control ionic motion . 31

A Lagrangian model of Copepod dynamics: clustering by escape jumps in turbulence 32

Ice formation and convection in the top layer of polar oceans . . . . . . . . . . . . . . 33

Homogeneous states in a gas of inelastic and rough hard spheres: The undriven anddriven cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Absorbed energy by shear thickening fluids confined in microfluidic patterns subjectedto impact tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Helicity and energy transfer in three dimensional turbulence . . . . . . . . . . . . . . 36

Particle trajectory entanglement in microfluidic channels . . . . . . . . . . . . . . . . 37

Emergent structures and dynamics in suspensions of active colloids . . . . . . . . . . 38

Amoeboid swimming in confined geometry . . . . . . . . . . . . . . . . . . . . . . . . 39

Flow of foam in a convergent channel . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Nematic microfluidics with structured channels . . . . . . . . . . . . . . . . . . . . . 41

Brownian motion near cell membranes . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Margination of active particles in the blood stream . . . . . . . . . . . . . . . . . . . 43

Shape and velocity distribution in a rotating cluster of superparamagnetic particles . 44

Magnetic microconvection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Experimental Evidence of Nonadditivity of Critical Casimir Forces . . . . . . . . . . . 46

Incidence of the particle size over the tortuosity in a porous medium using the latticeBoltzmann method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

A small-scale experimental set-up for processing-related materials characterization . . 48

Gyrotactic swimming in uniform vorticity . . . . . . . . . . . . . . . . . . . . . . . . 49

CFD modelling of flow behaviour in a membrane cross-flow filtration cell . . . . . . . 50

Small buoyant particles in turbulent flows . . . . . . . . . . . . . . . . . . . . . . . . 51

Impact of the Peterlin approximation on polymer dynamics in turbulent flows . . . . 52

Thermophoretic colloids, swimmers, and flows . . . . . . . . . . . . . . . . . . . . . . 53

From colloid phoresis to phoretic micromachines . . . . . . . . . . . . . . . . . . . . . 54

Breakup of finite size colloidal aggregates in turbulent flow investigated by 3D particletracking velocimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Two phase water management inside porous PEMFC anodes . . . . . . . . . . . . . . 56

II CONTENTS

CONTENTS

Lattice Boltzmann models for the simulation of flows through microchannels . . . . . 57

Effects of inertia in the steady-shear flow of disordered solids . . . . . . . . . . . . . . 58

Guiding catalytically active particles with chemically patterned surfaces . . . . . . . . 60

Inverse energy cascade in non-local helical shell-models of turbulence . . . . . . . . . 61

Bacteria swimming in high-molecular weight polymer: lambda-DNA . . . . . . . . . . 62

Two beam energy exchange on diffraction grating induced in liquid crystal cell withelectrically-driven boundary conditions . . . . . . . . . . . . . . . . . . . . . . . 63

Effective interactions between chemically active Janus colloids and surfaces . . . . . . 64

Rheology of polymer solutions over a wide range of concentrations . . . . . . . . . . . 65

Capillary rise in micro channels with smooth and patterned walls . . . . . . . . . . . 66

Finite-size effects in particle-laden turbulent channel flow in the dense regime . . . . . 68

Gravity waves in water covered by a viscous layer and disk-like impurities . . . . . . . 69

Intermittency in the Fractal Fourier Burgers Equation . . . . . . . . . . . . . . . . . 71

Platelet margination in tubular blood flow . . . . . . . . . . . . . . . . . . . . . . . . 72

Regularised sourcelets and stokeslets for phoretic problems . . . . . . . . . . . . . . . 73

Dynamics of flexible fibers in shear flows . . . . . . . . . . . . . . . . . . . . . . . . . 74

Purely-elastic flow instabilities in a microfluidic flow focusing device . . . . . . . . . . 76

Head-on collision between two spherical chemically active particles . . . . . . . . . . . 77

Multiscale Modeling of Transport in Confined Media . . . . . . . . . . . . . . . . . . 78

Digital Fourier Microscopy: a versatile tool for complex dynamics . . . . . . . . . . . 79

2D and 3D Migration and Proliferation of Cells and Cellular Tissues by Time-LapseMicroscopy and Image Analysis: a Transport Phenomena approach to ActiveBio-Soft-Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Angular Dynamics of a spheroid in shear at small Reynolds number . . . . . . . . . . 81

Lattice Boltzmann approach to liquid - vapour separation . . . . . . . . . . . . . . . 82

Quantifying the role of turbulence on droplet growth by condensation . . . . . . . . . 83

Microrheology in a hard-sphere colloidal glass: Simulations and Theory . . . . . . . . 84

Controlled generation of topological defects in nematic microfluidical environment . . 85

Effects of composition, water plasticization and pre-crystallization process on theflowability of model dairy powders . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Active particles at and close to fluid-fluid interfaces . . . . . . . . . . . . . . . . . . . 87

Copepod acceleration: statistical analysis from high speed camera measurements . . . 88

Pedestrian dynamics: accurate data collection and modeling . . . . . . . . . . . . . . 89

CONTENTS III

CONTENTS

Pedestrian dynamics: from pairwise interactions to large scale measurements . . . . . 90Adhesion strengths, shapes and the dynamics of red blood cell clusters at stasis and

in microcapillary flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Anomalous transport of circular swimmers in disordered structures: classical edge-

state percolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92Robust Energy Transfer Mechanism via Precession Resonance in Nonlinear Turbulent

Wave Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Emplacement of the lavaflow of Bardarbunga Iceland . . . . . . . . . . . . . . . . . . 94Non-Newtonian transport properties of granular suspensions under simple shear flow . 95Self-organized active agents in a fluid environment: hydrodynamics matters . . . . . . 96Translational and rotational temperatures of a granular impurity in a gas of inelastic

rough particles in the homogeneous cooling state . . . . . . . . . . . . . . . . . . 97Flow of interacting colloidal suspensions through a narrow channel . . . . . . . . . . . 98Self-assembly of colloidal bands driven by a periodic external field . . . . . . . . . . . 99Flow visualization of a particulate blood analogue reproducing the erythrocytes cell

free layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100Manipulation of long-term dynamics in a colloidal active matter system using speckle

light fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102A new microfluidic methodology to assess the haemocompatibility of magnetic

nanoparticles designed for theranostic applications . . . . . . . . . . . . . . . . . 103Perplexities of Cerebral Blood Flow and Oxygen Metabolism . . . . . . . . . . . . . . 105Complex turbulent swirling flow analysis . . . . . . . . . . . . . . . . . . . . . . . . . 106Instability of oscillatory pipe flow of wormlike micellar solutions . . . . . . . . . . . . 108Studying and controlling drop motion on inclined surfaces . . . . . . . . . . . . . . . 109Role of inertia in the rheology of amorphous systems: a finite element based elasto

plastic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor- Belt . . 111Numerical Analysis of blood flow in the common carotid artery bifurcation and influ-

ence of non-Newtonian blood rheological properties on blood flow . . . . . . . . 112Tumbling in an Extensional Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Dynamics of thin fluid films with thermal fluctuations . . . . . . . . . . . . . . . . . . 115

Index 116

IV CONTENTS

Introduction

Flowing matter lies at the crossroads between industrial processes, fundamental physics, en-gineering and Earth Sciences. Depending on the microscopic interactions, an assembly ofmolecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elasti-cally like a solid or behave in a complex manner. When the internal constituents are active,as for biological entities, one generally observes complex large-scale collective motions. Thephenomenology is further complicated by the invariable tendency of fluids to display chaos atthe large scales or when stirred strong enough. A fundamental understanding of flowing matteris still missing impeding scientific progress, effective control on industrial processes, as well asaccurate predictions of natural phenomena. Flowing matter frequently presents a tight couplingbetween small-scale structures and large-scale flow urging for a unifying approach. The Actionwill coordinate existing research efforts into a synergetic plan of collaborations and exchangesto develop an innovative multi-scale approach able to encompass the traditional micro-, meso-,and macro-scales descriptions. Breakthroughs in the understanding of flowing matter will im-pact on fundamental key scientific issues, such as the glass, the elasto-plastic and the jammingtransitions, as well as industrial applications including health, energy, cosmetics, detergents,food, paints, inks, oil and gas.

This book constitutes a compilation of the works presented in the international conferenceFlowing Matter 2016 covering the three main topics of the COST Action: complex fluids, activematter and complex flows. I hope you enjoy reading this book.

1

Invited Talks

3

2. Invited Talks

Mechanical Yield to Plastic Flow in Amorphous Materials

Itamar ProcacciaDepartment of Chemical Physics The Weizmann Institute of Science Rehovot 76100 Israel

Materials that exhibit a "yield" phenomenon response elastically to small strains or stresses,but at some critical value of the stress they yield mechanically and exhibit a complex plasticflow. The search of criteria to distinguish the properties of the material before and after theyield was long and futile; none of the standard signatures like correlation functions, Voronoitesselations or any other "structural" measure succeeded to clarify the difference between pre-yield and post-yield configurations. I will explain in this talk how to construct a new orderparameter that will allow us to show that the yield phenomenon is a bona-fide first orderthermodynamic phase transition, shedding an entirely new light on the phenomenon.

4

2. Invited Talks

Turbulence modeling for polymer solutions

F. T. Pinho1∗, M. Masoudian1, C. B. da Silva2

1Transport Phenomena Research Center, Mechanical Engineering Department Faculdade de Engenharia,

Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal,

[email protected],[email protected] 2IDMEC/IST, Universidade de Lisboa, Av. Rovisco Pais, 1049-001

Lisboa, Portugal, [email protected]

Sixty six years ago Toms1 reported the dramatic reduction in friction losses exhibited bysome polymer solutions in turbulent pipe flow as compared to the corresponding Newtonianflow. This finding triggered a wealth of research on drag reduction by polymer additives,followed by investigations with surfactant solutions, that continues up to this day and includesother canonical turbulent flows such as isotropic turbulence or planar jets. We review ourcurrent knowledge on the characteristics of such turbulent flows for polymers solutions,gathered both from experiments and direct numerical simulations, and proceed to present anoverview and characteristics of current turbulence models for engineering purposes. We alsooutline directions of research in the field both from fundamental and applied perspectives.

References[1] Toms, B. A. 1948. Some observations on the flow of linear polymer solutions through

straight tubes at large Reynolds numbers. Proc. 1st International Congress of Rheology, 2,135-141.

5

2. Invited Talks

Diffusive and convective surface (nano)droplets

Detlef LohseUniversity of Twente

Nanodroplets on a solid surface (i.e. surface nanodroplets or sessile nanodroplets) havepractical implications for high-throughput chemical and biological analysis, lubrications, lab-on-chip devices, and near-field imaging techniques. Oil nanodroplets can be produced on asolid-liquid interface in a simple step of solvent exchange in which a good solvent of oil isdisplaced by a poor solvent. We report on our experimental and theoretical investigation of theformation of nanodroplets by the solvent exchange process under well-controlled flow conditions.We found significant effects from the flow rate and the flow geometry on the droplet size. Wehave developed a theoretical framework to account for these effects. The main idea is thatthe droplet nuclei are exposed to an oil oversaturation pulse during the exchange process. Theanalysis gives that the volume of the nanodroplets increases with the Peclet number Pe of theflow as ∝ Pe3/4, which is in good agreement with our experimental results.

We will also report on surface nanodroplet formation on patterned surfaces of all kinds,which changes the growth or shrinkage mode of the nanodroplets. In particular, we will showhow nanodroplets nucleate at the rim of spherical cap microstructures on a substrate, due to apulse of oversaturation supplied by a solvent exchange process. We find that, while growing atthe rim of the microcap, the nanodroplets self-organize into highly symmetric arrangements,with respect to position, size, and mutual distance. The angle between the neighboring dropletsis 4 times the ratio between the base radii of the droplets and the spherical caps. We showand explain how the nanodroplets acquire the symmetrical spatial arrangement during their

6

2. Invited Talks

competitive growth and why and how the competition enhances the overall growth rate of thenucleated nanodroplets. This mechanism behind the nanodroplet self-organization promises asimple approach to control the location of droplets with a volume down to attoliters.

Finally, we will show that gravity can have an effect of the formation of surface droplets.Counter-intuitively, it can also have an effect on the dissolution of small immersed sessiledroplets. We study the dissolution process of long-chain alcohol (of various types) sessiledroplets in water is studied, disentangling diffusive and convective contributions. The lattercan arise for high solubilities of the alcohol, as the density of the alcohol-water mixture isthen considerably less than that of pure water, giving rise to buoyancy driven convection.The convective flow around the droplets is measured, using micro-particle image velocimetry(µPIV) and the schlieren technique. When non-dimensionalizing the system, we find a universalSh ∼ Ra1/4 scaling relation for all alcohols (of different solubilities) and all droplets in theconvective regime. Here Sh is theSherwood number (dimensionless mass flux) and Ra theRayleigh number (dimensionless density difference between clean and alcohol-saturated water).This scaling implies the scaling relation τ ∝ R5/4 of the convective dissolution time τ , whichis found to agree with experimental data. We show that in the convective regime the plumeReynolds number (the dimensionless velocity) of the detaching alcohol-saturated plume followsRep ∼ Sc-1Ra5/8, which is confirmed by the µPIV data. Here, Sc is the Schmidt number.The convective regime exists when Ra > Rat, where Rat = 12 is the transition Ra- numberas extracted from the data. For Ra < Rat and smaller, convective transport is progressivelyovertaken by diffusion and the above scaling relations break down.

ReferencesDetlef Lohse and Xuehua Zhang, Surface nanobubbles and nanodroplets, Rev. Mod. Phys.

87, 981-1035 (2015);Xuehua Zhang, Ziyang Lu, Huanshu Tan, Lei Bao, Yinghe He, Chao Sun, and Detlef Lohse,

Formation of surface nanodroplets under controlled flow conditions, Proc. Nat. Acad. Sci. 112,9253-9257 (2015).

Shuhua Peng, Detlef Lohse, and Xuehua Zhang, Spontaneous pattern formation of surfacenanodroplets from competitive growth, ACS Nano 9, 11916-11923 (2015).

Erik Dietrich, Sander Wildeman, Claas Willem Visser, Kevin Hofhuis, E. Stefan Kooij,Harold J. W. Zandvliet, and Detlef Lohse, Role of natural convection in the dissolution ofsessile droplets, J. Fluid Mech., submitted (2016).

7

2. Invited Talks

Bio-inspired sensing of complex flows

Maarja KruusmaTallinn University of Technology

This talk addresses sensing and interpreting complex flows from the perspective of biologicalorganisms, fish. All 30 000 fish species have a special flow sensing organ called a lateral line. Itis a dual modality sensing system capable of sensing flow speed and differential pressure aroundthe fish body. We have developed several sensor systems, robots and field deployable probesto investigate the interaction between the fish and its environment as well as to develop newkinds of robots capable of sensing and interpreting the flow information. First the engineeringapproach, which takes loose inspiration of lateral line sensors is described. Then we demonstratethe first flow-sensing underwater robot that is capable of sensing flow and controlling itself withrespect to the flow in order to swim upstream, hover in the wake of the object and save energyin a reduced flow zone. We then also show how this information about complex flows canbe classified and correlated to physical locations in the flow that are later recognizable for therobot based on their hydrodynamic signatures. We then describe measurements and informationprocessing in natural environments, rivers and man-made fish passes. The goal of this work isto study flow patterns from "fish perspective" and correlate physical measurements in the flowwith fish behaviour. We hope that it will help us understand how fish navigate rivers and howto construct fish passes at hydropower plants so that they facilitate fish upstream migration.

8

2. Invited Talks

Rheology of dense suspensions of non colloidal spheres in

Newtonian and yield-stress fluids

Elisabeth GuazzelliAix-Marseille Université

Dense suspensions are materials with broad applications both in industrial processes (e.g.waste disposal, concrete, drilling muds, metalworking chip transport and food processing) andin natural phenomena (e.g. flows of slurries, debris and lava). Despite its long research historyand its practical relevance, the mechanics of dense suspensions remain poorly understood.A frictional approach, which stems from the rheology of dry granular materials, has beensuccessfully applied to suspensions using an original pressure-imposed shear cell (Boyer,Guazzelli, and Pouliquen 2011). This alternative way of looking at suspensions provides a wayto circumvent the divergence observed in volume-imposed rheometry and yields examinationof the rheology close to the jamming transition. This has been recently applied to suspensionsof non-Brownian spheres in yield-stress fluids. Accurate measurements of the shear stress andparticle normal stress are favorably compared with a model based on scaling arguments andhomogenization method (Dagois-Bohy, Hormozi, Guazzelli, and Pouliquen 2015).

ReferencesBoyer, F., Guazzelli, E., and Pouliquen, O. (2011). Unifying Suspension and Granular Rheol-ogy. Physical Review Letters, 107(188301).Dagois-Bohy, S., Hormozi, S., Guazzelli, E., and Pouliquen, O. (2015). Rheology of dense sus-pensions of non-colloidal spheres in yield-stress fluids. Journal of Fluid Mechanics, 776, R2.

9

2. Invited Talks

Hydrodynamics and phase behaviour of biologically active

suspensions

Suzanne FieldingDepartment of Physics, Durham University, Science Laboratories, South Road, Durham. DH1 3LE

Following a brief pedagogical introduction to the field of biologically active suspensions, wediscuss recent research results for the phase behaviour and rheology of these fluids.

In the first part of the talk we report simulations of a continuum model for active fluidsin two dimensions (2D). We focus on extensile materials and find that steady shear bands,previously shown to arise ubiquitously in 1D for the active nematic phase at small (or indeedzero) shear rate, are generally replaced in 2D by more complex flow patterns that can bestationary, oscillatory, or apparently chaotic. The consequences of these flow patterns for time-averaged steady-state rheology are examined.

In the second part we discuss particle based simulations with hydrodynamics of a suspen-sion of active disks squirming through a Newtonian fluid. We explore numerically the full rangeof squirmer area fractions from dilute to close packed and show that "motility induced phaseseparation" (MIPS), which was recently proposed to arise generically in active matter, andwhich has been seen in simulations of active Brownian disks, is strongly suppressed by hydro-dynamic interactions. We give an argument for why this should be the case and support it withcounterpart simulations of active Brownian disks in a parameter regime that provides a closercounterpart to hydrodynamic suspensions than in previous studies.

10

2. Invited Talks

Microorganisms in flow

Roman StockerETH Zurich

Bacteria and phytoplankton live in watery habitats that, more often than not, are char-acterized by fluid flow, from creeping fluid motion to turbulence. When ubiquitous biologicalfeatures of microorganisms are considered - their often elongated shape, their ability to swim,their asymmetric distribution of mass - a rich set of unexpected consequences emerges, frompatchiness in cell distribution to biases in directional migration to enhanced surface attach-ment. I will share recent insights from our work on some of these processes, which not onlyopen a wealth of new problems for the physicist working on complex flows and active matter,but also provide the biologist with new insights into the life of microorganisms in realistic fluidenvironments.

11

2. Invited Talks

A scalable platform for functional nanomaterials

Jie Feng1, and Howard Stone1, Luben N. Arnaudov2 and Simeon D. Stoyanov3

1Department of Mechanical and Aerospace Engineering, Princeton University, Princeton NJ 08544, USA

2Unilever Research and Development, 3133AT Vlaardingen, The Netherlands

Bubble bursting at interfaces plays an important role in a spectrum of physical andbiological phenomena, from foam evolution to mass transport across various interfaces1-5.Recently, bubble bursting at an air/oil/water-with-surfactant compound interface was foundto disperse submicrometer oil droplets into the water column6. Inspired by this observation,here we propose a new top-down platform to generate functional oil-in-water nanoemulsions.We demonstrate scaled-up synthesis of nanoemulsions with stability for days, which offers theflexibility of further treatments and functionalization. By placing functional materials in theappropriate phase, we also document that the bubbling system has the capability to producenanoemulsions encapsulating functional materials, such as quantum dots, silica nanoparticlesand lipid molecules. Considering the simplicity and energy efficiency of the new bubblingplatform, together with the diversity of products and the potential for mass production, ourone-step a new toolbox for generating (multi-)functional nanoemulsions and nanoparticles.

References

1. Vandewalle, N., Lentz, et. al. Avalanches of popping bubbles in collapsing foams, Phys.Rev. Lett. 86 , 179-182 (2001).2. Prentice, P., et. al. Membrane disruption by optically controlled microbubble cavitation, Nat.Phys. 1, 107-110 (2005).3. Russell, L. M., et.. al. Carbohydrate-like composition of submicron atmospheric particles

12

2. Invited Talks

and their production from ocean bubble bursting, Proc. Natl. Acad. Sci. U.S.A. 107 , 6652-6657 (2010).4. Bird, J. C., et. al. Daughter bubble cascades produced by folding of ruptured thin films,Nature, 465 , 759-762 (2010).5. Lhuissier, H. et. al. Bursting bubble aerosols. J. Fluid Mech. 696 , 5-44 (2012).6. Feng, J. et al. Nanoemulsions obtained via bubble-bursting at a compound interface Nat.Phys. 10 , 606-612 (2014).

13

2. Invited Talks

How elastic instabilities in the flow of entangled polymer

solutions explain an unexpected increase in oil recovery

Andrew. M. HoweVisiting Researcher Cambridge University BP Institute and Department of Chemical Engineering Department.

This presentation will describe the flow behaviour of high MW viscoelastic polymersporous media. In such complex confined environments, the solutions exhibit unstable flow(dependent on polymer MW, apparent shear rate and local geometry) at low Reynolds number.The fluctuations in pressure gradient cause an apparent thickening and lead to an enhanceddisplacement of capillary trapped oil ganglia. In the production of crude oil, most of theoil recovery occurs during the process of water (brine) "flooding". In this process, brine ispumped into the reservoir at injection wells so as to displace oil towards production wells.In situations where the oil viscosity is greater than that of water the flood front becomesunstable, leading to a fingering / flow non-uniformity such that large oil-containing reservoirvolumes are bypassed. Water-soluble polymers are often added to the flooding solution toincrease viscosity and hence uniformity of the flow profile ("sweep efficiency") leading toincreased production. The production from the swept regions ("displacement efficiency") isrationalised in terms of the flow capillary number describing the balance between the pressuregradient and the interfacial forces that "trap" the oil in the rock pores. Recently, flooding witha polymer solution that exhibits elastic properties has been reported to increase displacementefficiency, resulting in a sustained doubling of the recovery enhancement over that fromconventional viscous polymer flooding. Flooding with viscoelastic polymer solutions is claimedalso to increase recovery more than expected from changes in capillary number alone. This

14

2. Invited Talks

increase in displacement efficiency by viscoelastic polymers was attributed to changes in thesteady state flow profile and enhancements in oil stripping and oil-thread formation. However,researchers in universities and in the oilfield industry have expressed significant doubts thata genuine effect is observed, or that improvements in displacement efficiency occur withinfield-applicable flow regimes. In this talk, I will demonstrate that flooding with viscoelasticpolymer solutions can indeed increase recovery more than expected from changes in capillarynumber. The improvement in displacement efficiency arises from fluctuations in flow at lowReynolds Number. This behaviour, known as elastic turbulence, an elastic flow instability, isan effect previously unrecognised in oil recovery. The effect may be obtained at field-relevantflow rates and provides an underlying mechanism explaining both the enhanced capillarydesaturation curves and the observation of apparent flow thickening for these viscoelasticsolutions in porous media. , I will describe a combination of core flooding, micromodel flow,and rheometric studies, contrasting flow and recovery using viscous and viscoelastic polymersolutions. The circumstances under which viscoelasticity is beneficial will be demonstrated.The findings reveal an unexpected dependence on solution composition. The data lead to amechanism that may be used to explain the observations of improved displacement efficiency,are applicable to the design of formulations for enhanced oil recovery by polymer flooding andreveal why the improvement is not seen for all viscoelastic polymer floods. The studies werecarried out in Schlumberger Research, Cambridge UK between 2012 and 2015 and particularacknowledgements are owed to Drs Andrew Clarke and Jonathan Mitchell.

Wang, D., Wang, G. & Xia, H. Large Scale High Visco-Elastic Fluid Flooding in the FieldAchieves High Recoveries. SPE Conference, pp. SPE 144294-MS, 2011.Wang, D., Xia, H., Yang, S. & Wang, G. The Influence of Visco-elasticity on Micro Forces andDisplacement Efficiency in Pores,Cores and in the field. SPE Conference, pp. SPE 127453-MS,2010.Vermolen, E. C., Haasterecht, M. J. T. & Masalmeh, S. K. A systematic study of thepolymer visco-elastic effect on residual oil saturation by core flooding. SPE Conference, pp.SPE169681-MS, 2014.A. Groisman and V. Steinberg, Elastic turbulence in a polymer solution, Nature, 405, 53, 2000.Seright, R. S., Fan, T., Wavrik, K. & Balaban, R. d. C. New insights into polymer rheology inporous media. SPE Journal, pp. SPE129200-PA, 2011.

15

2. Invited Talks

Delshad, M. et al. Mechanistic Interpretation and Utilization of Viscoelastic Behaviourof Polymer Solutions for Improved Polymer-Flood Efficiency. SPE Conference, pp. SPE113620-MS, 2008.Clarke, A., Howe, A.M, J.Mitchell, J.Staniland, L.A.Hawkes. Mechanism of anomalouslyincreased oil displacement with aqueous viscoelastic polymer solutions. Soft Matter, 11, 3536,2015.Howe, A. M., Clarke, A. & Giernalczyk, D. Flow of concentrated viscoelastic polymer solutionsin porous media: effect of MW and concentration on elastic turbulence onset in variousgeometries. Soft Matter, 11, 6419, 2015.A.Clarke, A.M.Howe, J.Mitchell, J.Staniland, L.A.Hawkes. How Viscoelastic Polymer FloodingEnhances Displacement Efficiency, SPE-174654, SPE Journal, in press.Mitchell J., Lyons K., Howe A.M., Clarke A., Viscoelastic polymer flows and elastic tur-bulence in three-dimensional porous structures. Soft Matter, 2015, Advance Article, DOI:10.1039/C5SM01749A.

16

2. Invited Talks

Single and collective fiber dynamics in microflows

Anke LindnerUniv. Paris Diderot Laboratoire de Physique et Mécanique des Milieux Hétérogénes (PMMH)

The flow of complex suspensions is ubiquitous in nature and industrial applications. Theirnon-Newtonian character is due to flow-induced orientation, rearrangement, or deformation ofmicroscopic objects suspended in simple fluids. The understanding and control of the effectiveflow properties of such complex suspensions relies thus on a precise understanding of the fluidstructure interactions at the microscopic level. We have recently built a micro fabrication andflow platform that gives at the same time precise control of particle and flow properties andthat allows for the observation of microscopic particle dynamics as well as the measurement ofeffective suspension properties. In this talk I will specifically address the question of transportdynamics of anisotropic objects in confined micro-flows. These objects range from rigid toflexible fibers and finally active E-coli bacteria. The role of shape, flexibility and activity on thetransport dynamics will be addressed and we will show that interaction with bounding wallscan lead to unexpected dynamics. Some examples of collective dynamics in the suspensions ofsuch particles will be discussed.

17

Other Contributions

19

3. Other Contributions

Earthquake statistics inferred from plastic events in

soft-glassy materials

Federico Toschi1, Roberto Benzi2 and Jeannot Trampert1Eindhoven University of Technology, Eindhoven, The Netherlands

2University of Roma, Tor Vergata

We present a new approach for generating synthetic earthquake catalogues based on thephysics of soft glasses. Our continuum approach that is based on the Lattice Boltzmann methodproduces yield-stress materials. If the material is stimulated while being kept below the yieldstress plastic events occur and share strong similarities with seismic events. By a a suitabledefinition of displacement we show that plastic events obey a Gutenberg-Richter law withexponents similar to the ones of real earthquakes. Our approach is fully self-consistent and allquantities can be calculated at all scales without the need of ad-hoc friction or statistical laws.The proposed approach may lead to new insight in the understanding of the physics connectingthe micro- and macro-scale in earthquakes dynamics.

20


Phase and precession evolution in the Burgers equation

Miguel D. Bustamante1, Michele Buzzicotti2, Brendan Murray1 and Luca Biferale21School of Mathematics and Statistics, University College Dublin, Belfield, Dublin 4, IRELAND

2Department of Physics, University of Rome Tor Vergata, 00133 Roma, ITALY

We present a phenomenological study of the phase dynamics of the one-dimensional stochas-tically forced Burgers equation evolved on a fractal Fourier set. We uncover a connection be-tween coherent structures in real space and the evolution of triads in Fourier space. Real spacestructures are associated with entangled correlations amongst the phase precession frequenciesand the amplitude evolution of triads in Fourier space. As a result, triad precession frequenciesshow a non-Gaussian distribution with multiple peaks and fat tails, and there is a significantcorrelation between triad precession frequencies and amplitude growth. Links with dynamicalsystems approach are briefly discussed, such as the role of unstable critical points in state space.By allowing D, the fractal dimension of the underlying Fourier set, to take values below 1, weobserve a depletion of intermittency and a reduction of the correlation between the growth ofFourier mode amplitudes and the precession frequencies of triad phases.

21


Clustering and Turbophoresis in a Shear Flow without

Walls

Stefano Musacchio, Elena Piretto, Guido BoffettaUniversité de Nice Sophia Antipolis, Laboratoire J.A. Dieudonné, Parc Valrose, 06108 Nice, France

We investigate the spatial distribution of inertial particles suspended in the bulk of a tur-bulent inhomogeneous flow. By means of direct numerical simulations of particle trajectoriestransported by the turbulent Kolmogorov flow, we study large and small scale mechanismsinducing inhomogeneities in the distribution of heavy particles. We discuss turbophoresis bothfor large and weak inertia, providing heuristic arguments for the functional form of the particledensity profile. In particular, we argue and numerically confirm that the turbophoretic effectis maximal for particles of intermediate inertia. Our results indicate that small-scale fractalclustering and turbophoresis peak in different ranges in the particles’ Stokes number and theseparation of the two peaks increases with the flow’s Reynolds number.

22


Confinement and Clustering of Floaters in Stratified

Turbulence

G. Boffetta, F. DeLillo, S. Musacchio, A. SozzaUniversity of Torino, Via Pietro Giuria 1, 10125 Torino, Italy

Turbulence and stratification are ubiquitous in the upper ocean and their interplay is crucialfor the comprehension of the aquatic ecosystems. In particular particles of density different fromthe surrounding fluid are known to generate inhomogeneous distribution even in incompressibleflows. Some impressive examples of accumulation of particles in the ocean are the formationof thin phytoplankton layers and the marine snow aggregates. One proposed mechanism, ofpossible relevance for non-swimming species (such as diatoms) is based on buoyancy forcein stratified flow. We derive a new model, valid within the Boussinesq approximation, forthe dynamics of small inertial particles in stratified turbulence, in presence of a mean lineardensity profile. By means of extensive direct numerical simulations, we investigate the statisticaldistribution of particles as a function of the two dimensionless parameters of the problem:the stratification of the flow and the relaxation time of the particles. We find that verticalconfinement of particles is mainly ruled by the degree of stratification, with a weak dependencyon the particle properties. Conversely, small scale fractal clustering depends on the particlerelaxation time and is only slightly dependent on the flow stratification. We discussed theimplications of our findings for the formation of thin phytoplankton and marine snow.

23


Relaxation dynamics of functionalized colloids on

attractive substrates

Cristóvão DiasCentro de Física Teórica e Computacional, Faculdade de Ciências da Universidade de Lisboa, Campo Grande,

Ed-C8, 1749-016 Lisboa

Particle-based simulations are performed to study the post-relaxation dynamics of func-tionalized (patchy) colloids adsorbed on an attractive substrate. Kinetically arrested structuresthat depend on the number of adsorbed particles and the strength of the particle-particle andparticle-substrate interactions are identified. The radial distribution function is characterizedby a sequence of peaks, with relative intensities that depend on the number of adsorbed par-ticles. The first-layer coverage is a non-monotonic function of the number of particles, withan optimal value around one layer of adsorbed particles. The initial relaxation towards thesestructures is characterized by a fast (exponential) and a slow (power-law) dynamics. The fastrelaxation timescale is a linearly increasing function of the number of adsorbed particles in thesubmonolayer regime, but it saturates for more than one adsorbed layer. The slow dynamicsexhibits two characteristic exponents, depending on the surface coverage.

24


Lagrangian analysis of rotating Rayleigh-Bénard

turbulence

Alards, K.M.J., Rajaei, H., Kunnen, R.P.J., Toschi, F., Clercx, H.J.H.Eindhoven, University of Technology, De Rondom 70, 5612 AP, Eindhoven

Transitions between turbulent states occur in rotating Rayleigh-Bénard convection (RRBC)by changing rotation, which is known to change the flow structure and the heat transport. In thisstudy we want to characterize these different states of turbulence using Lagrangian statisticsof tracer particles. RRBC is modeled using DNS and tracer particles that perfectly follow theflow are included. Lagrangian statistics of 1e6 particles are measured in the form of velocity,acceleration and temperature pdfs for different rotation rates. The influence of rotation on theflow structure and heat transport is analyzed. Statistics obtained in the cell center and nearthe top and bottom plate are compared in order to investigate the influence of the boundarylayers on RRBC. On top of that the results are compared with experiments, in which neutrallybuoyant particles are tracked in a cylindrical RRBC setup. An excellent agreement betweenexperiments and numerics is found.

25


Effects of viscoelasticity on droplet dynamics and break-up

in microfluidic T-Junctions : a Lattice Boltzmann study

Anupam Gupta and Mauro SbragagliaDepartment of Physics, INFN, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma,

Italy

The effects of viscoelasticity on the dynamics and break-up of liquid threads in a microfluidicT-junctions are investigated using numerical simulations of dilute polymeric solutions for awide range of Capillary numbers (Ca), i.e., changing the balance between the viscous forcesand the surface tension at the interface. A Navier-Stokes (NS) description of the solvent basedon the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finiteextensible non-linear elastic dumbbells with the closure proposed by Peterlin (FENE-P model).The various model parameters of the FENE-P constitutive equations, including the polymerrelaxation time and the finite extensibility parameter, are changed to provide quantitativedetails on how the dynamics and break-up properties are affected by viscoelasticity.

26


Local synchronization of inertial beads in a ionic

time-dependent chaotic flow

D. Garaboa-Paz, A.P. Muñuzuri, and Vicente Pérez MuñuzuriGroup of Nonlinear Physics, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain

The motion of catalyst-carrying inertial beads immersed in a ionic time-dependent turbulentflow is studied in terms of the transport barriers developed in the fluid. It is well knownthat inertial particles in a turbulent flow may cluster together and their motion can differmarkedly from Lagrangian particle dynamics [1]. Here, two set of particles, inertial (beads) andLagrangian (ions) are mixed together in a flow while they exchange chemical properties.

Catalyst beads immersed in a chemical medium [2] has been shown to synchronize [3]. Inour case, the time-dependent flow gives rise to synchronized regions separated by the transportbarriers. We analyze the roles of beads size and densities in terms of the exchange rate betweenthe beads and the ionic flow, and the Finite Time Lyapunov Exponents characterizing the flow.The coherence of the population of oscillators is determined in terms of the order parameterintroduced by Kuramoto.

References[1] V. Pérez Muñuzuri, Phys. Rev. E 91, 052906 (2015); D. Garaboa-Paz and V. Pérez

Muñuzuri, Nonlin. Processes Geophys. 22, 571-577 (2015).[2] T. Amemiya, T. Ohmori, M. Nakaiwa, and T. Yamaguchi, J. Phys. Chem. A 102, 4537-

4542 (1998).[3] A.F. Taylor, M.R. Tinsley, F. Wang, Z. Huang, and K. Showalter, Science 323, 614-617

(2009).[4] G. Ghoshal, A.P. Muñuzuri and J. Pérez-Mercader. Nature Scientific Reports (2015)

DOI: 10.1038/srep19186.

27


Modelling of Residence Time Dispersion of Falling Droplets

Kevin Cronin1 and Song Miao21 Dept. of Process & Chemical Engineering, UCC, Cork, Ireland

2 Teagasc, Food Research Centre, Moorepark, Ireland

The fall of liquid droplets under gravity through a gas to achieve a desired level of heatand mass transfer is a common process in many chemical engineering unit operations. Becauseof atomizer characteristics, such droplets are poly-dispersed in size. Furthermore, residencetime of the droplets is also distributed. The combined and interacting effects of dispersion indroplet size and dispersion in droplet residence time cause variation in the final moisture contentand temperature of the resulting spray dried powders. This may have serious product qualityimplications. A model of droplet residence time that incorporates the deterministic effects ofgravity and drag force is proposed. Stochastic effects in the motion of the droplets are includedby the use of a kinetic dispersion parameter. This is a log-normally distributed random variablewhose statistics and their dependence on droplet size are obtained by experiments. Hence thejoint probability density function of residence time and droplet diameter can be obtained, thestatistics of residence time quantified and also the correlation between droplet diameter andresidence time found.

28


Measurements of diffusion in anisotropic fluids

Mojca Vilfan, Hana Majaron, Darja Lisjak and Alenka MerteljJ. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

We experimentally observed diffusion of microparticles is anisotropic fluids. Two samplecases were studied Ð nematic liquid crystals and liquid crystalline ferrofluids. Separate diffusioncoefficients were determined, depending on the direction of motion relative to the orientation ofthe director. Apart from standard nematic liquid crystals also recently discovered ferromagneticliquid crystals were investigated. In these materials, magnetic platelets are introduced into anematic liquid crystal forming a stable ferromagnetic suspension. The second example is tert-butyl alcohol with added magnetic platelets. At lower concentrations, the suspension exhibitsanisotropic behaviour due to magnetic interactions between the platelets, however, the collectivefluctuational dynamics is observed only for concentrations larger than 10 %vol.

Both studied systems are very responsive to external magnetic fields. Fields as low as 10mT suffice to reorient magnetic moments coupled with liquid crystalline ordering, while simul-taneously suppressing the long range director fluctuations. On the other hand, an increase influctuations can be achieved by introducing instabilities into the nematic order by switching thedirection of the magnetic field into antiparallel orientation regarding the sample magnetisation.We observed particle diffusion in the presence of an external magnetic field and investigatedthe influence of fluctuations on diffusion dynamics.

29


Manipulating surface plasmons in graphene ribbons with

liquid crystal

V. Yu. Reshetnyak1,2, T. J. Bunning3 and D. R. Evans31Physics Faculty, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine

2Dipartimento SIMAU, Universitá Politecnica delle Marche, Ancona, Italy3Air force Research Laboratory, Material and Manufacturing Directorate, Wright-Patterson Air Force Base,

USA

Propagation of surface plasmons in a conducting layer depends on the dielectric propertiesof media confining the layer. Liquid crystals (LC) are known to change their dielectric tensorwhen reoriented. We suggest using LC to control the plasmons in graphene ribbons. The liquidcrystal layer is placed on top of the graphene ribbons grating. Externally applied voltagereorients LC director and hence changes the LC dielectric tensor, which finally affects thesurface plasmons in graphene ribbons. Our modelling involves the following elements: liquidcrystal director spatial profile, electric field distribution in LC, and electromagnetic wavepropagation through the sandwich: liquid crystal-graphene ribbons - dielectric substrate. Wefind that by using liquid crystal one can tune the plasmons in graphene ribbons.

AcknowledgementsV. Yu. Reshetnyak thanks the EOARD/STCU Grant P652 and COST ActionMP1305 as wellas the Universitá Politecnica delle Marche, Ancona, Italy for a visiting scientist fellowship.

30


Entropic electrokinetics: How to use geometrical

constraints to control ionic motion

Ignacio Pagonabarraga MoraDepartment of Fundamental Physics, Phyiscs Faculty, University of Barcelona, Barcelona, Spain

When particles are suspended in an electrolyte confined between corrugated charged sur-faces, electrokinetic flows lead to a new set of phenomena such as particle separation, mixingfor low-Reynolds micro- and nano-metric devices and negative mobility. Such phenomena arisedue to the interplay between the electrostatic double layer and the corrugated geometrical con-finement and that they are magnified when the width of the channel is comparable to the Debyelength.A systematic, simplified theoretical treatment allows us to understand the physical ori-gin of such phenomena therefore shading light on their possible relevance in a wide variety ofsituations, ranging from nano- and micro-fluidic devices to biological systems.

31


A Lagrangian model of Copepod dynamics: clustering by

escape jumps in turbulence

H. Ardeshiri, E. Calzavarini, F. G. Schmitt, F. Toschi, S. SouissiUniversity of Lille 1, Science and technology, Cité Scientifique, 59655, Villeneuve d’Ascq Cedex

Planktonic copepods are small crustaceans that have the ability to swim by quick powerfuljumps. Such an aptness is used to escape from high shear regions, which may be caused eitherby flow perturbations, produced by a large predator (i.e. fish larvae), or by the inherent highlyturbulent dynamics of the ocean. Through a combined experimental and numerical study, weinvestigate the impact of jumping behaviour on the small-scale patchiness of copepods in aturbulent environment. Recorded velocity tracks of copepods displaying escape response jumpsin still water are here used to define and tune a Lagrangian Copepod (LC) model. The model isfurther employed to simulate the behaviour of thousands of copepods in a fully developed hydro-dynamic turbulent flow obtained by direct numerical simulation of the Navier-Stokes equations.First, we show that the LC velocity statistics is in qualitative agreement with available exper-imental observations of copepods in turbulence. Second, we quantify the clustering of LC, viathe fractal dimension D2. We show that D2 can be as low as ∼ 2.3 and that it critically dependson the shear-rate sensitivity of the proposed LC model, in particular it exhibits a minimum ina narrow range of shear-rate values. We further investigate the effect of jump intensity, jumporientation and geometrical aspect ratio of the copepods on the small-scale spatial distribution.

32


Ice formation and convection in the top layer of polar

oceans

A. Abba, F. De Santi, P. Olla and L. ValdettaroISAC-CNR, Dip. Fisica, Universitá di Cagliari, Monserrato (Cagliari), Italy

We discuss the behavior of some standard models of ice formation in a few limit regimesof ice formation rate, heat flux from the atmosphere, and characteristic rise velocity of theice crystals in the water column. The analysis will first focus on the constraints imposed bythe conservation laws and the thermodynamics of the process, in the case of a homogeneousdomain. It will then shift to the real problem, i.e. the modification that ice production is goingto induce on convection in a water column cooled from the top.

33


Homogeneous states in a gas of inelastic and rough hard

spheres: The undriven and driven cases

F. Vega Reyes and A. SantosUniversidad de Extremadura, Departamento de Física, E-06071 Badajoz, Spain

We study a granular gas of inelastic rough spheres for two prototypical homogeneous states:(i) the undriven free cooling state and (ii) the steady state driven by a spatially uniformstochastic white-noise force, the latter acting on the translational particle velocities, by addingthem a random impulse. In both cases an analytical solution of the corresponding velocitydistribution function is worked out from a Sonine polynomial expansion that displays energynon-equipartition between the translational and rotational modes, translational and rotationalkurtoses, and translational-rotational velocity correlations. By comparison with numerical so-lutions of the Boltzmann kinetic equation (by means of the Direct Simulation Monte Carlomethod) we show that our analytical solutions provide good general descriptions that are semi-quantitatively and quantitatively accurate in the undriven and driven states, respectively, forwide ranges of inelasticity and roughness. We also find three important features that make theforced granular gas steady state very different from the homogeneous cooling state. First, themarginal velocity distributions are always close to a Maxwellian. Second, there is a continu-ous transition to the purely smooth limit (where the effects of particle rotations are ignored).And third, the angular translational-rotational velocity correlations show a preference for aquasiperpendicular mutual orientation ("lifted-tennis-ball" behavior). None of these propertiesare held in the undriven case.

34


Absorbed energy by shear thickening fluids confined in

microfluidic patterns subjected to impact tests

Francisco J. Galindo-Rosales, Bruna Pires, Sergio Martínez-Aranda and Laura Campo-DeañoCEFT, Faculdade de Engenharia da Universidade do Porto, Portugal.

This work is framed on the development of CorkSTFfluidics composites, a new conceptof energy-absorbing composites based on cork micro-agglomerated engraved with patternsof microchannels and filled with a shear thickening fluids. When subjected to an impact,the part of the energy is dissipated by the simultaneous contribution of the cork and thefluid, which will flow through a well-defined geometry, and the fluid-structure Interactions.It has been observed that the amount of energy dissipated by the composite depends onseveral parameters: the rheological properties of the shear thickening fluid (STF), the shapeof the microfluidic patterns and the separation between them. In this work we present asystematic study analysing the performance of the different CorkSTFfluidics compositesvarying these three variables of design. Results confirmed that balancing these variables is notstraightforward and they must be chosen wisely, otherwise CorkSTFfluidics composites mayshow worsened mechanical response compared with the cork micro-agglomerate alone.

AcknowledgementsAuthors would like to acknowledge financial support from FCT, COMPETE andFEDER through project IF/00190/2013/CP1160/CT0003 and grants IF/00148/2013 andIF/00190/2013.

35


Helicity and energy transfer in three dimensional

turbulence

Ganapati SahooDept. of Physics and INFN, University of Roma, Tor Vergata, Via della Ricerca Scientifica 1, Roma, Italy.

Helicity is an inviscid invariant of the three dimensional Navier-Stokes equations like energy.It plays a vital role in the dynamics of energy transfer in three dimensional turbulence. Based onthe helicity content of the triads participating in the dynamics, the direction of the transfer ofthe energy in a fluid flow could be either from the large scales to small scales or in the oppositedirection. Using a Galerkin decimation of helical Fourier modes I will show how helicity playsa significant role in the transfer of energy among the scales and the resulting intermittency inthe system. These results highlight the importance of some characteristics of homogeneous andisotropic flows with a wide range of applications: these include rotating and conducting flowsof strong geophysical and astrophysical relevance.

36


Particle trajectory entanglement in microfluidic channels

Alvaro Marin, Massimiliano Rossi, Christian J. KahlerBundeswehr University Munich, Neubiberg, Germany

Suspensions in motion can show very complex and counterintuitive behavior, particularly athigh concentrations. In this talk we unravel an overlooked phenomenon occurring when a diluteparticle solution is forced to travel in a narrow channel (only a few times the particle size).At critical interparticle distances, particles tend to interlace their trajectories, only bondedby hydrodynamic interactions. While classical studies on non-Brownian self-diffusivity reportaverage particle displacements of fractions of the particle diameter, the trajectories observed inour system show displacements of several particle diameters. Additionally, entangled particlesseem to "synchronize" their motion with others located at several particle diameters. Particletrajectory statistics are obtained from the experiments for different shear rates and particlesizes showing the same results in wide range of parameters. The results are then comparedwith particle dynamics simulations and analyzed to elucidate the nature of the hydrodynamicinteractions entering into play. The reported phenomenon could be applied to promote advectivemixing in micro-channels or particle/droplet self-assembly.

37


Emergent structures and dynamics in suspensions of active

colloids

Andrea Scagliarini, Ignacio PagonabarragaHelmholtz Institute Erlangen-Nürnberg for Renewable Energies, 90429 Nürnberg,Germany.

Active fluids, such as suspensions of self-propelled particles , are a fascinating example of SoftMatter displaying complex collective behaviours which provide challenges in non-equilibriumStatistical Physics. The recent development of techniques to assemble miniaturized devices hasled to a growing interest for micro and nanoscale engines that can perform autonomous motion("microrobots"), as, for instance, self-phoretic colloids, for which the propulsion is inducedby the generation of a chemical species in a reaction catalyzed at the particle surface. Weperform a mesoscopic numerical study of suspensions of self-phoretic colloids. We show that, atchanging the sign of the phoretic mobility (which accounts for the colloid-solute interactions),the system switches from a cluster phase to a state with slowed dynamics. We find that thecluster size distribution follows an exponential behaviour, with a characteristic size growinglinearly with the colloid activity, while the density fluctuations grow as a power-law with anexponent depending on the cluster fractal dimension.We single out hydrodynamic interactions,showing that their effect is to work against cluster formation. For positive µ, we observe thatcolloids tend to reach an ordered state on a triangular lattice.

38


Amoeboid swimming in confined geometry

Hao Wu, Marine Thiebaud, Weifan Hu, Alexander Farutin, Salima Rafai, Mingchih Lai,Philippe Peyla, Chaouqi Misbah

Laboratoire Interdisciplinaire de Physique (LIPhy) - CNRS, 140 Avenue de la Physique - BP 87, Domaine

universitaire de Grenoble, 38402 Saint Martin d’Héres - FRANCE

Many eukaryotic cells undergo frequent shape changes (described as amoeboid motion) thatenable them to move forward. We investigate the effect of confinement on a minimal model ofamoeboid swimmer. A complex picture emerges: i) The swimmerÕs nature (i.e. either pusheror puller) can be modified by confinement thus suggesting that this is not an intrinsic prop-erty of the swimmer. This swimming nature transition stems from intricate internal degreesof freedom of membrane deformation. (ii) The swimming speed might increase with increas-ing confinement before decreasing again for stronger confinements. (ii) A straight amoeboidswimmerÕs trajectory in the channel can become unstable, and ample lateral excursions of theswimmer prevail. This happens for both pusher and puller-type swimmers. For weak confine-ment, these excursions are symmetric, while they become asymmetric at stronger confinement,whereby the swimmer is located closer to one of the two walls. In this study, we combinenumerical and analytical analyses.

39


Flow of foam in a convergent channel

Benjamin DolletInstitut de Physique de Rennes, UMR 6251 CNRS/Université Rennes 1

As a model system for the plastic flow of complex fluids, we study experimentally the flowof a foam confined as a bubble monolayer between two plates through a convergent channel. Wequantify the velocity, the distribution and orientation of plastic events, and the elastic stress,using image analysis. We use two different soap solutions: a sodium dodecyl sulfate (SDS)solution, with a negligible wall friction between the bubbles and the confining plates, and amixture containing a fatty acid, giving a large wall friction. We show that for SDS solutions,the velocity profile obeys a self-similar form which results from the superposition of plasticevents, and the elastic deformation is uniform. For the other solution, the velocity field differsand the elastic deformation increases towards the exit of the channel. We discuss and quantifythe role of wall friction on the velocity profile, the elastic deformation, and the rate of plasticevents.

40


Nematic microfluidics with structured channels

Jure Aplinc1 and Miha Ravnik1,21 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana,

Slovenia2 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

In this talk, we discuss the flow of nematic liquid crystal in the microfluidic channels of var-ious geometrical shapes and porosities. The distinction of nematic liquid crystals from isotropicfluids lies in the orientational ordering of liquid crystal molecules caused by their anisotropicshape. This anisotropy notably affects also the flow of nematic liquid crystals. In the presenceof flow velocity gradients, the backflow coupling causes the reorientation of the director field.

We demonstrate backflow driven formation of various flow states using numerical modelling,including defects. Specifically we use hybrid lattice Boltzmann modelling to successfully describethe backflow coupling between the material flow and the nematic orientational ordering.

Finally we discuss the experimental realisation of such systems, with particular focus towardstunable soft matter photonic materials.

41


Brownian motion near cell membranes

Abdallah Daddi-Moussa-Ider, Achim Guckenberger, and Stephan GekleBiofluid Simulation and Modeling. Universitaet Bayreuth, 95440 Bayreuth, Germany

Using a two-dimensional Fourier transform technique, we study the translational Brownianmotion of a small solid particle near a realistically modeled red blood cell. We compute atleading order, i.e. when the particle is far away from the elastic membrane, the correction to thefrequency dependent mobility tensor. We find that hydrodynamic interactions create a memoryeffect in the particle dynamics. A generalized Langevin equation is therefore applied in orderto evaluate the mean-squared displacement in the overdamped regime. At the intermediatetime scales, we find that the particle undergoes a subdiffusion, with a local scaling exponentas low as 0.9 in the parallel direction, and as low as 0.8 in the perpendicular direction. A goodagreement is found between the theoretical predictions and the numerical simulations that weperform using a completed double layer boundary integral equation method.

42


Margination of active particles in the blood stream

Stephan GekleUniversität Bayreuth, 95440 Bayreuth, Germany

Stiff particles flowing in a suspension of highly deformable red blood cells are pushed tothe channel walls, an effect called margination. In recent years, intense research efforts havebeen devoted to investigate the influence of particle shape and size on this physiologicallyvery important effect. Here we use a combination of Boundary Integral and Lattice Boltzmannsimulations to study the margination of active particles which has not been investigated so far.We focus on two types of particles: (i) stiff particles moving under the influence of an externalforce and (ii) oscillating microbubbles which periodically vary in size driven by an externalultrasound pressure field.

43


Shape and velocity distribution in a rotating cluster of

superparamagnetic particles

Andrej Vilfan, Dusan Babic, Jure Dobnikar, Gasper Kokot, Tomaz Mohoric, Natan OstermanJ. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Colloidal suspensions of superparamagnetic beads form a lattice of rotating vortices whenexposed to a precessing magnetic field below the magic angle. This process is an example ofdynamic self-assembly. The resulting shape of magnetic clusters is determined by the time-averaged dipole-dipole interaction between magnetic particles. In addition, the rotating mag-netic field exerts a torque on a vortex which drives the rotation around the vertical axis. Weidentify the the finite relaxation rate of the particle magnetization, which lags behind the ro-tating field, as the main source of the torque. A second contribution to the torque can originatefrom collective deformations of the cluster as a whole.

To predict the shape and angular velocity of a vortex, we propose an analytical modelwhich describes the vortex as a ferrofluid drop and the effect of the rotating field as a spatiallyhomogeneous torque density. While the shape equation is exactly solvable, we use the bound-ary element method to determine the velocity profile. The results show good agreement withexperimentally measured sizes and angular velocities.

44


Magnetic microconvection

A. Cebers,G. Kitenbergs,A. Tatulcenkovs,K. ErglisUniversity of Latvia, Zellu 23, Riga, LV-1002, Latvia

Fingering instability on the interface between miscible magnetic and non-magnetic fluids inHele-Shaw cell is studied both experimentally and theoretically. It is shown that the Brinkmanmodel with account of ponderomotive forces of the self-magnetic field of magnetic fluid givesquantitative and qualitative description of the observed phenomena - dependence of the fingervelocity on the magnetic field strength, threshold value of the field strength and other. It isfound that in horizontal Hele-Shaw cells important role is played by the gravitational forcesdue to density difference of magnetic and non-magnetic fluids.

45


Experimental Evidence of Nonadditivity of Critical

Casimir Forces

Giovanni VolpePhysics Department, Bilkent University, 06800 Cankaya/Ankara, Turkey

From gravitation to electromagnetism, the fundamental physical interactions are additive:for instance, the force exerted on a probe electric charge in an homogeneous medium by twoother charges equals the sum of the forces exerted by each of them separately. In more com-plex situations, however, effective interactions take hold — and these forces are not necessarilyadditive. Accordingly, a crucial issue is whether, and to what extent, genuinely many-body ef-fects are present. For example, from the confinement of a fluctuating field effective long-rangedforces between two microscopic objects may result at the micrometer scale. A notable exampleare critical Casimir forces acting on micrometer-sized particles immersed in a binary liquidmixture near its critical (demixing) point confining the concentration fluctuations. These forcesare theoretically predicted to be nonadditive, but experimental evidence for the correspond-ing many-body effects is still lacking. Here, we report the direct experimental measurement ofsuch effects. Using holographic optical tweezers (HOTs) and digital video microscopy (DVM)to probe in situ the forces acting on spherical colloids immersed in a critical mixture of waterand 2,6-lutidine in various geometrical configurations, we observe that the critical Casimir forceexerted on a probe colloid by two other colloids differs from the sum of the forces exerted bythem separately. These many-body effects are controlled by adjusting the criticality of the mix-ture, e.g. by tuning its temperature or by changing the surface properties of the particles. Sinceinteractions between microscopic particles in fluids are central to a wide spectrum of physical,chemical and biological phenomena, the insight we provide here might prove useful in a diverserange of applications, including controlling microscopic self-assembly of colloids, complex col-lective behaviours, as well as phase and biomimetic behaviours of micro- and nanoparticles —considering in particular that many-body effects are expected to become even more importanton the nanoscale.

46


Incidence of the particle size over the tortuosity in a

porous medium using the lattice Boltzmann method

Mayken Espinoza, Martin Andersson, Bengt SundénLund University, Department of Energy Sciences, 22363, Lund, Sweden

Tortuosity is a measure of the geometric complexity of the porous media. Knowing thetortuosity value of the porous media is helpful to get detailed information about the fluidbehavior at microscale. In order to calculate the tortuosity, the velocity field of the fluid troughthe porous media is determined using the lattice Boltzmann method (LBM). The particle sizeof the obstacles is varied, keeping the porosity of the material as a constant. As a result, arelationship to determine the particle diameter as a function of the number of particles for aspecific porosity value is given, and the dependence of the tortuosity with respect to the mainflow direction is demonstrated.

47


A small-scale experimental set-up for processing-related

materials characterization

Paulo F. Teixeira, José A. Covas and Loic HilliouInstitute for Polymers and Composites/I3N, Universidade do Minho, Departamento de Engenharia de

Polímeros, Campus de Azurém, Guimarães, Portugal

As polymers progressively meet more stringent requirements in terms of processing and per-formance, it is often necessary to developed complex material systems while minimizing costsand time-to-market. Thus, it seems useful to make available fast response characterization toolsthat although using small amounts of sample, are still capable of conveying adequate data onthe correlations between rheological response, process-induced material structure and productproperties. For this purpose, a prototype small-scale single / twin-screw extrusion system ofmodular construction, with outputs in the range 30-300 g/h, was coupled to a rheo-opticalslit die designed to be able to measure shear viscosity and normal-stress differences, as well asperforming rheo-optical experiments, namely small angle light scattering (SALS) and polarizedoptical microscopy (POM). The extruder is equipped with ports that allow sample collection,in order to subsequently evaluate the evolution of melting and mixing, morphology, or chemicalconversion, whichever relevant. Also, downstream equipment is available, so that the engineeringproperties of the extrudate can be evaluated. As an example, processing of a PS/PMMA indus-trial blend and the properties of extruded sheets will be studied. The morphological evolutionalong the extruder, the flow-induced structures developed and the corresponding rheologicalcharacteristics are presented, together with the mechanical and structural characteristics of thesheets. Future developments will also be discussed.

48


Gyrotactic swimming in uniform vorticity

G. Boffetta, M. Borgnino, M. CenciniUniversity of Torino, Department of Physics, 10125 Torino, Italy

We study the dynamics of swimming gyrotactic cells in a uniform rotating environment.By means of analytical and numerical methods we characterize the swimming behavior on thebasis of physical and biological parameters. The results are used to analyze the outcome ofexperiments with different gyrotactic species.

49


CFD modelling of flow behaviour in a membrane cross-flow

filtration cell

D. Dzhonova, I. Tsibranska, S. VlaevInstitute of Chemical Engineering, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

The present work is part of study on membrane separation for energy-saving productionof value added bio-products. It is connected with development of models of integrated bio-processes including membrane separation for concentration, fractionation and purification ofproducts from the biotechnology, where external membrane cells of cross-flow operation modeare used. This investigation is also based on previous experience in integrating solid-liquidextraction with nanofiltration with the purpose of concentration/separation of antioxidantsfrom the group of polyphenols and flavonoids from extracts of natural products.This work is focused on CFD modelling of the flow behaviour in an experimental flat-sheetmembrane cell for cross-flow filtration, where the solution enters the cross-flow cell tangentiallyfrom the cell wall and exits the cell from the top center, providing fluid recirculation. Theaim is studying the optimal geometry parameters and hydrodynamic regimes for preventionof membrane fouling and modelling the conditions of the processes in view of industrialapplication.

Keywords: membrane cross-flow filtration, modelling of complex flows, biologically active ma-terials, energy-saving recovery

50


Small buoyant particles in turbulent flows

Enrico CalzavariniUniversity of Lille, CNRS, FRE 3723, LML, Laboratoire de M«ecanique de Lille, F 59000 Lille, France

In recent years a great amount of work has been devoted to the study of accelerationstatistics of inertial particles in turbulence. Systematic comparisons between experiments anddirect numerical simulations have been carried out in order to understand which hydrodynamicseffects play a key role in particle dynamics. Studies have focused mostly on the effect of particlemass density and on the particle size effect. To a less extent the influence of shape has beeninvestigated. Much less studies have been dedicated to the effect of gravity induced buoyancyon particle statistics. The reason for this is that for sufficiently sustained turbulent flows thiscontribution becomes negligible. This is however not the case in many real case situations or forinstance in experimental setups with light buoyant particles. With an input from experimentsof small bubbles in turbulent flow, we numerically investigate the effect of finite Froude numberon the acceleration statistics of small particles with different density as the one of the fluid.

51


Impact of the Peterlin approximation on polymer

dynamics in turbulent flows

Dario Vincenzi, Prasad Perlekar, Luca Biferale and Federico ToschiLaboratoire J.A. Dieudonné, Université Nice Sophia Antipolis, Parc Valrose, Nice, France

We study the impact of the Peterlin approximation on the statistics of the end-to-end separa-tion of polymers in a turbulent flow. The FENE and FENE-P models are numerically integratedalong a large number of Lagrangian trajectories resulting from a direct numerical simulation ofthree-dimensional homogeneous isotropic turbulence. Although the FENE-P model yields re-sults in qualitative agreement with those of the FENE model, quantitative differences emerge.The steady-state probability of large extensions is overestimated by the FENE-P model. Thealignment of polymers with the eigenvectors of the rate-of-strain tensor and with the directionof vorticity is weaker when the Peterlin approximation is used. At large Weissenberg numbers,both the correlation times of the extension and of the orientation of polymers are underesti-mated by the FENE-P model.

52


Thermophoretic colloids, swimmers, and flows

Marisol RipollTheoretical Soft Matter and Biophysics, Institute of Complex systems, Forschungszentrum Jülich, Germany

Colloid thermophoresis refers to the directed motion of macromolecules in the presence ofa temperature gradient [1]. Self-propelled motion can be induced for example in the cases ofJanus or dimers colloidal particles with asymmetric properties [2,3]. In these cases, one half ofthe particle can be heated to a fixed temperature producing a radially symmetric temperaturegradient. The thermophoretic properties of the other half produce then a propulsion againstor towards the heated part, such that the asymmetric microparticle becomes a microswimmer.These self-propelled particles can have properties of puller, pushers or neutral swimmers [4].Besides the colloidal drift, the temperature gradient also induces a flow of the surroundingsolvent [5]. This flow is responsible for example of the long-ranged hydrodynamic attractionbetween colloidal particles near a heated boundary wall. Thermophoretic flows are also inducedin the proximity of walls that experience a tangential tempereature gradient which can beused to generate diverse flow patterns. I will outline recent work performed by means of amesoscopic simulation technique known as multiparticle collision dynamics simulations (MPC)[6,7].

1. Lüsebrink, D., Yang, M. and Ripoll, M., J. Phys.: Condens. Matter 24, 284132, 2012.2. Jiang, H. R., Yoshinaga, N., and Sano, M., Phys. Rev. Lett., 105, 268302, (2010).3. Yang, M. and Ripoll, M., Phys. Rev. E, 84, 061401, (2011).4. Yang, M., Wysocki, A., and Ripoll, M., Soft Matter 10, 6208, 2014.5. Yang, M. and Ripoll, M., Soft Matter 9, 4661, 2013.6. Malevanets, A. and Kapral, R., J. Chem. Phys. 110, 8605Ð8613, 1999.7. Lüsebrink, D. and Ripoll, M., J. Chem. Phys. 136, 084106, 2012.

53


Rheo-optical characterization of sheared DNA hydrogels

L. Tunesi1, T. Roversi2, T. Bellini1, and G. Zanchetta1

1 Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Universitá di Milano (Italy)

2 Dipartimento di Scienze per gli Alimenti, la Nutrizione e l’Ambiente, Universitá di Milano (Italy)

Hydrogels built from DNA are an attractive class of materials, with applications rangingfrom drug delivery to molecular recognition. Their structure and mechanical properties can betuned by chemical, covalent cross-linking, or by clever design of "physical" cross-links based onselective Watson-Crick base pairing [Peng et al., Nature Nanotechnology 109, 816 (2012)]. Evensimple systems of entangled helices display a complex mechanical response, also involving thepartial ordering of the strands, which we can characterize through their optical anisotropy. Westudy the relaxation mechanisms, upon application of shear deformations, in networks of 103base pairs-long DNA helices. In a wide concentration range, the solutions are viscoelastic butalso lay in the Isotropic-Nematic coexistence region [Merchant and Rill, Biophys.J. 73, 3154(1997)]. Indeed, while they are almost isotropic at rest, when sheared they develop strong tran-sient birefringence. We thus compare their stress response with the local alignment propertiesthrough a shear cell coupled to a polarized microscope and a fast camera. We investigate theeffect of DNA concentration and thermal history, which in turn determines the degree of DNAhybridization and the entanglement and topology of the resulting networks [Orakdogen et al.,Macromolecules 43, 1530 (2010]. Overall, we find that stress relaxation and reorientation arecharacterized by several distinct, yet coupled, timescales, involving diffusion and large-scalerearrangements. We are currently extending our combined opto-rheological approach to DNAhydrogels with more complex structures [Bellini et al., PNAS 109, 1110 (2012)] and to otherbiopolymer networks like nanocellulose.

54


Breakup of finite size colloidal aggregates in turbulent flow

investigated by 3D particle tracking velocimetry

Matthaus Babler1, Debashish Saha2, Markus Holzner3, Miroslav Soos4, Beat Luthi5, AlexLiberzon6, Wolfgang Kinzelback3

1KTH Royal Institute of Technology, Sweden2Eindhoven University of Technology, the Netherlands

3ETH Zurich, Switzerland4University of Chemistry and Technology Prague, Czech Republic

5Photrack AG, Zurich, Switzerland6Tel Aviv University, Israel

Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropicturbulence where their breakup is recorded by 3D partilce tracking velocimetry (3D-PTV). Theaggregates have an open structure with fractal dimension around 2.2 and their size is 1.4 ±0.4 mm which is large compared to the Kolmogorov length scale η = 0.15 mm of the turbulentflow. 3D-PTV allows for the simultaneous measurement of aggregate trajectories and the fullvelocity gradient tensor along their pathlines which enables us to access the Lagrangian stresshistory of individual breakup events. We found no consistent pattern that relates breakup tothe local flow properties. Also the correlation between the aggregate size and shear stress atthe point of breakage is found to be weaker when compared with the correlation between sizeand drag stress. The analysis suggests that aggregates are mostly broken due to accumulationof drag stress over a time-lag of order Kolmogorov time scale. This finding is explained by thefact that the aggregates are large which gives their motion inertia and which increases the timefor stress propagation and stress dissipation inside the aggregate. Furthermore, it is found thatthe scaling of the largest fragment and the accumulated stress at breakup follows an earlierestablished power law obtained from laminar nozzle experiments. This indicates that despitethe large size and the different type of hydrodynamic stress, the microscopic mechanism thatcause breakup is consistent over a wide range of aggregate size and stress magnitude.

55


Two phase water management inside porous PEMFC

anodes

M. Andersson, S. Beale, W. Lehnert, B. SundénDepartment of Energy Sciences, Lund University, Sweden & Institute of Energy and Climate Research

Electrochemical Process Engineering (IEK-3), Research Center Jülich, Germany

Before work to improve PEMFCs and PEMECs can commence, the reaction and transportmechanisms of liquid water droplets must be identified and a link established between accu-mulation of water and the performance characteristics. The numerical descriptions describingtwophase flow distribution and its interaction with the porous material inside PEMFCs andPEMECs are today simplified, i.e., neglecting too many phenomena to archive a reasonabledescription and understanding of the physical twophase-multiscale-multiphysics transport andreaction phenomena. Our research focuses on the reaction and transport mechanisms of waterdroplets in FC and EC porous electrodes and connecting channels. In general, a low pressuredifference across the flow field is desired because lower auxiliary energy demand, e.g., for aircompression. On the other hand, a certain pressure drop is necessary to remove condensatefrom the flow field channels. These opposite requirements lead to the following question: Whatis the minimum pressure drop and respective gas flow rate to remove the condensate in order toprevent flooding of the channels which would lead to an undersupply of gases in some regionsof the cell?

56


Lattice Boltzmann models for the simulation of flows

through microchannels

Victor E. Ambrus, Victor SofoneaCentre for Fundamental and Advanced Technical Research, Romania Academy, Timisoara Branch, RO

300223, Timisoara, Jud. Timis, Romania

We consider the two-dimensional non-isothermal Couette and Poiseuille flows at non-negligible values of the Knudsen number (Kn). Using lattice Boltzmann methods based onquadrature methods, we demonstrate that, at finite Kn, the simulation results converge as thequadrature order (Q) is increased. We highlight the dramatic decrease in the value of Q requiredfor convergence when half-space quadratures are used to correctly implement diffuse reflectionboundary conditions on the channel walls.

57


Effects of inertia in the steady-shear flow of disordered

solids

Alexandre Nicolas, Jorg Rottler, Francesco Puosi and Jean-Louis BarratCentro Atómico Bariloche & CONICET, Bariloche, Argentina (previously at LIPhy, Université

Grenoble-Alpes & CNRS, Grenoble, France)

Inertia matters in liquid flows. Its presence in the Navier-Stokes equations of motion of fluidsleads to a rich phenomenology that vanishes in the overdamped limit of viscous flow. Despitethis major discrepancy, the effect of inertia is rarely heeded in the flow of disordered solids

This neglect may surprise, since these materials span the whole range of damping strengths(from the most overdamped - e.g., foams and emulsions - to the most underdamped - e.g.metallic glasses). We have addressed this outstanding question by means of numerical simula-tions and our work [1] sheds light on the large variations of the macroscopic rheology with theinertial quality factor (which measures the - inverse - relative damping strength). Out of thesevariations, through a proper identification of the relevant nondimensional parameters, we haverationalised the effect of the inertial quality factor and a simple (but quantitatively accurate)picture emerges: there are two well defined damping regimes, each of which can be described byonly two parameters (for given interactions between particles). In the overdamped regime, therheology is controlled by the bath temperature and the Weissenberg number (i.e., the competi-tion between elastic and viscous forces), while the underdamped rheology only depends on thekinetic temperature of the material and the shear rate multiplied by the Einstein’s vibrationfrequency; the impact of the damping is thus amalgamated to a temperature effect.

When looking at more complex flows, the macroscopic rheology might not be sufficient anda more detailed understanding of the flow may be required. It is widely accepted that theflow of disoredered solids features swift localised rearrangements of particles, known as sheartransformations, which burst out in an essentially elastically deforming medium. These sheartransformations can, in turn, trigger new rearrangements at a distance, via the long-rangedeformation of the elastic medium that they induce.

Shear transformations are the building blocks of virtually all mesoscale rheological modelsconcerned with these materials, but so far the elastic deformations that they induce are generallycomputed under very coarse assumptions, including the uniformity of the medium and the

58


neglect of all inertial effects. To remedy these deficiencies, we have proposed a very simpleFinite-Element (FE)-based method, which captures the effects of elastic heterogeneity as wellas inertia. The method has been validated through a detailed comparison of the response to ashear transformation with molecular dynamics simulations, from which the (viscous and elastic)parameters used in FE were directly extracted, and paves the way to computationally efficientand realistic rheological models, in which structural disorder and inertial effects are accountedfor.

[1] A. Nicolas*, J.-L. Barrat, J. Rottler* (equal contribution), Effects of inertia on thesteady-shear rheology of disordered solids. Submitted to Physical Review Letters. arXiv preprintarXiv:1508.06067, 2015. [2] A. Nicolas, F. Puosi, H. Mizuno, J.-L. Barrat (2015). Elastic con-sequences of a single plastic event: towards a realistic account of structural disorder and shearwave propagation in models of flowing amorphous solids. Journal of the Mechanics and Physicsof Solids, 78, 333-351.

59


Guiding catalytically active particles with chemically

patterned surfaces

W.E. Uspal, M.N. Popescu, S. Dietrich, and M. TasinkevychMax Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany

Catalytically active Janus particles in solution create gradients in the chemical compositionof the solution along their surfaces, as well as along any nearby container walls. The former maylead to self- soutdiffusiophoresis, while the latter can give rise to the “dual” response, chemi-osmosis, giving an additional contribution to self-motility. Chemi-osmosis strongly dependson the nature of the molecular interactions between the diffusing chemical species and thewall. We show analytically, using an approximate "point-particle" approach, that by chemicallypatterning a planar substrate (e.g., by using two different materials), one can direct the motionof Janus particles: the induced chemi-osmotic flows can cause particles to either "dock" at aninterface between the two materials, or to follow a chemical stripe. These theoretical predictionsare confirmed by full numerical calculations. Generically, docking occurs for particles that tendto move away from their catalytic caps, while stripe-following occurs in the opposite case. Thephysical mechanisms governing this behavior are elucidated by our analysis.

60


Inverse energy cascade in non-local helical shell-models of

turbulence

Massimo De Pietro, Luca Biferale, Alexei MailybaevUniversitá degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy

Following the exact decomposition in eigenstates of helicity for the Navier-Stokes equationsin Fourier space we introduce a modified version of helical shell-models for turbulence withnon-local triadic interactions. By using both analytical argument and numerical simulation weshow that there exists a sub-class of models with elongated shell interactions that exhibits astatistically stable inverse energy cascade. Using also data from direct numerical simulationsof helical Navier-Stokes equations we further support the idea that energy transfer mechanismin fully developed turbulence is the result of a strong entanglement among different triadicinteractions possessing different transfer mechanisms.

61


Bacteria swimming in high-molecular weight polymer:

lambda-DNA

C. Devailly, V.A. Martinez, A. Dawson, J. Schwarz-Linek, W. PoonThe University of Edinburgh, James Clerk Maxwell Building, Mayfield Road, Edinburgh, EH9 3JZ

In the past few years, E.coli has become a model swimmer in the active matter field.Numerous studies focus on the swimming in water but bacteria as Escherichia coli (E.Coli)usually live in viscoelastic media such as mucus in intestine tract. Mucus is a strong viscoelasticmaterial with shear-thinning properties containing long polymer chains as proteins and DNA.It has been suggested recently [1] that in a solution of PolyVinylpirrolidone PVP 360kDa,small and fast rotating flagella (40nm thickness rotating at 100Hz) create a local high shearrate (104 Hz) resulting in a polymer-free channel from its surrounding, while the slow rotatingbody (1um x 2um rotating at 20Hz) of the bacterium observe the viscosity of the polymersolution. Thus Bacteria body and flagella observe two different environments .Here, we perform experiments of swimming E.coli in a solution of lambda DNA. The polymercoils are about the length of the body bacteria itself. By using Differential Dynamic microscopyand Dark Field Microscopy analysis, we show that neither the velocity nor the rotation ofthe body is modified by increasing DNA concentration while the bulk viscosity increase bya factor of 10. These phenomena are particular to active particles, as Brownian diffusion ofnon-swimming bacteria is dependent on bulk viscosity as expected. Moreover, non-swimmingbacteria accumulate in a pattern with a characteristic length scale the value of which increaseswith DNA concentration.These results open the way to a better understanding of active particles in a polymer solution- which is nowadays only possible with swimming bacteria -, but also to a new type ofmicrorheology measurement using the fast rotating flagella as a probe.

References[1] Vincent A. Martinez et al. PNAS vol. 111 no. 50, 17771-17776 (2014).

62


Two beam energy exchange on diffraction grating induced

in liquid crystal cell with electrically-driven boundary

conditions

I. P. Pinkevych1, S. I. Subota1, V. Yu. Reshetnyak1, D. R. Evans21Physics Faculty, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine

2Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base,

USA

We study energy exchange between two coherent light beams incident onto nematic liquidcrystal (LC) cell with photorefractive substrates. Space charge field arising in photorefractivesubstrates penetrates into the LC cell, causing director periodic reorientation, and hencecreating a diffraction grating [1]. In present work we show that induced director gratingis a result of summation of two inphase gratings: flexoelectric grating arising due to thephotorefractive field interaction with the LC flexopolarization, and boundary driven gratingarising due to the director easy axis modulation at the LC cell walls caused by photorefractivefield. Each light beam diffracts from the induced grating, leading to energy gain and losswithin each beam. We solved equations for the LC director linked with Maxwell’s equationsfor light beams propagation, and calculated gain coefficient. It is shown that magnitude ofthe boundary driven grating and gain coefficient for this grating increase with increase ofthe director anchoring energy at the cell substrates. Magnitude of the flexoelectric gratingdecreases with the anchoring energy increase but gain coefficient for the flexoelectric gratinghas non-monothonic dependence on the anchoring energy. The total gain coefficient maximumshifts towards higher grating spacing with increase of both the anchoring energy and strengthof the director easy axis modulation.

References[1] Reshetnyak V.Yu., Pinkevych I.P., Cook G., Evans D. R., and T.J. Sluckin, Phys. Rev. E,81, 031705(1-15), 2010.

AcknowledgementsThe work was partially supported by the COST Action MP1305 and EOARD Grant P649.

63


Effective interactions between chemically active Janus

colloids and surfaces

M. N. Popescu, W. E. Uspal, M. Tasinkevych, P. Malgaretti, S. DietrichMax Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany

The area of chemically active colloids, capable of self-motility by extracting chemical freeenergy from their surroundings via promoting catalytically activated chemical, has received sig-nificant interest in the last decade [1,2]. Such active colloids induce hydrodynamic and chemicalfields that decay with the distance from the particle in a similar manner [3]. Therefore, whenthe active colloids are in the vicinity of walls, other particles, or fluid-fluid interfaces, a rich,complex behavior, emerges from the interplay of the two fields (see, e.g., Refs. [4,5]).

Focusing on a simple model of diffusiophoresis of spherical active Janus colloids [3], wediscuss here several examples of effects due to the spatial confinement, such as, e.g., theemergence of "sliding" and "hovering" states near a bounding solid surface [5] or effectiveattraction/repulsion to a fluid interface.

Referencies1. R.F. Ismagilov et al, Angew. Chem., Int. Ed., 41, 652 (2002).2. W.F. Paxton et al, JACS 126, 13424 (2004); J.R. Howse et al, Phys. Rev. Lett. 99, 048102(2007).3. R. Golestanian et al, New J. Phys. 9, 126 (2007).4. R. Soto and R. Golestanian, Phys. Rev. Lett. 112, 068301 (2014); O. Pohl and H. Stark,Phys. Rev. Lett. 112, 238303 (2014).5. William Uspal et al, Soft Matter 11, 434 (2015).

64


Rheology of polymer solutions over a wide range of

concentrations

Wilco M.H. Verbeeten, Gerrit W.M. Peters, Frank P.T. BaaijensUniversidade de Burgos, Campus Rio Vena, E-09006 Burgos, Spain

The investigation deals with the modelling of the flow behaviour of aqueous random coilmacromolecular solutions using non-linear viscoelastic models. Still quite often, researchersand scientists use General Viscous Fluid models to describe the rheology of such viscoelasticfluids, e.g. the Cross model. Although these types of models do an excellent job in modellingsteady state simple shear viscosity, they are unable to describe the other three phenomenaof viscoelasticity, i.e. time dependence, normal stresses in shear, and different behaviour inshear and elongation. Furthermore, these models are not able to describe satisfactorily thelinear viscoelastic behaviour measured by dynamic oscillation experiments. Thus, when morecomplex flows have to be analyzed, i.e. flows where material elements experience various types ofdeformations in a transient sense rather than steady state, these General Viscous Fluid modelsdo not suffice and more complex non-linear viscoelastic models are necessary.

The experimental linear viscoelastic, and transient and steady state shear data of variouspolysaccharide solutions can be quantitatively predicted by the eXtended Pom-Pom non-linearviscoelastic model. Quite often, they can also be described with other (phenomenological) net-work models, such as Phan-Thien Tanner and Giesekus models. These models are also capableof describing quantitatively commercial polymer melts.

For viscoelastic solutions, quantitative agreement is even accomplished over a broad range ofconcentrations, from dilute to semi-dilute regimes, using a single set of parameters. For this, asimple model is used to describe the concentration dependence of the relaxation time spectrum,based on a superposition principle similar to the time-temperature-superposition.

Due to their proven performance in finite element simulations, these non-linear viscoelasticconstitutive equations could help to improve predictive modelling of time-dependent complexflow problems.

65


Capillary rise in micro channels with smooth and

patterned walls

H. Javed1, F. F. Ouali1, G. McHale2, N. J. Shirtcliffe3 and M. I. Newton1

1School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK2 Faculty of Engineering and Environment, Northumbria University, Ellison Place, Newcastle upon Tyne NE1

8ST, UK3Faculty of Technology and Bionics, Hochschule Rhein-Waal, D-47533, Kleve, Germany

Micro-channels find many applications in various fields, e.g. in diagnostic testing andDNA manipulation and in micro-reactors. Imbibition into such channels can be forced orfree via the phenomenon of capillarity [1,2]. In the latter case, surface chemistry controls thehydrophobicity/ hydrophilicity of wall, but imbibition also depends on surface area. In thiswork, we focus on the interplay of surface structure and surface chemistry in determining howcapillary rise and imbibition occurs.Micro-channels (130-350 µm deep and 400-600 µm wide) were fabricated in SU-8 on glasssubstrates using photolithography. Imbibition and capillary rise of polydimethylsiloxanePDMS oils of varying viscosities were investigated using a high speed camera. The positionof the meniscus of the liquid was measured using image analysis software. Single and parallel"smooth" open channels and "rough" channels (symmetric saw-tooth type walls to giveincreased surface area) were investigated. The texture of the micro-channel is characterisedby a roughness parameter, r, defined as the fractional increase in the wall solid/liquid areaas compared to its projected area and varies experimentally from r =1 ("smooth" channels)to r =3. The width of the channel is increased with roughness in such a way as to keep itsaverage value constant, thus keeping the same average channel volume flow and allowing adirect comparison with the smooth channels. Here an "open" channel means the oil contactedthe base and side walls of the channel, but the oil’s upper surface was free to air and not incontact with a solid wall.The results show that for plane ("smooth") walls, the capillary rise followed the same trendas with capillary tubes. However, over time the meniscus was preceded by precursor fingers ofcornerrunning liquid along the internal corners defined by where the bottom of the channeland a side wall meet [3,5]. Measurements on "rough" walls found that the observed equilibriumheight increased with increasing r (i.e. surface area for capillary pull) as expected. Increasing

66


wall roughness also was found to decrease the prominence of the corner-running fingers. Thedata are fitted numerically and analytically using the viscous-gravitational model [3] modifiedto take into account of the increase in the capillary force with roughness, resulting from the in-crease in wall surface area, but which assumes that roughness does not alter viscous dissipation.

References[1] Lucas, R., Kolloid Z 23, pp.15-22 (1918).[2] Washburn, E. W., Physical Review 17, pp. 273-283 (1921).[3] Ouali, F. F., McHale, G., Javed, H., Trabi, C., Shirtcliffe, N. J., and Newton, M. I.,

Micro- Nano-fluidics, 15, pp 309-326 (2013).[4] Fries, N., and Dreyer, M., Journal of Colloid and Interface Science 320, pp. 259-263

(2008); 327, pp. 125-128 (2008).[5] Bico, J., and Quéré, D., Journal of Colloid and Interface Science 247, pp. 162-166 (2002).

67


Finite-size effects in particle-laden turbulent channel flow

in the dense regime

Pedro Costa, Francesco Picano, Luca Brandt and Wim-Paul BreugemDelft University of Technology, Laboratory for Aero and Hydrodynamics, 2628 CA Delft, The Netherlands

Particle-laden turbulent flows appear widely in environmental and industrial contexts. Inmany cases the suspension is dense and the particles have a size comparable to or larger thanthe smallest length scale of the flow (i.e., have a finite size). Fully-resolved direct numericalsimulations (DNS) of dense particle-laden flows have recently become possible and providedetailed insight in such flows at the particle scale and beyond. Our DNS makes use of anefficient Immersed Boundary Method (IBM) combined with a soft-sphere collision model andlubrication corrections for short-range inter-particle interactions. We have performed DNS ofturbulent plane channel flow of dense suspensions of neutrally-buoyant finite-size spheres ata fixed bulk Reynolds number of 12,000 and a solid volume fraction of 20%. The particlesize was varied between 10 and 20 viscous wall units, corresponding to 640,000 and 80,000particles, respectively. Results show that the particles increase drag to a value higher thanwhat is expected considering only the suspension effective viscosity. In the conference we willpresent detailed statistics of these simulations and discuss scaling considerations that accountfor the finite-size effect of the particles.

68


Gravity waves in water covered by a viscous layer and

disk-like impurities

Francesca De Santi, Piero OllaUniversity of Cagliari Department of Physics, 09042 Cagliari, Italy

The propagation of ocean waves can be affected by the presence of materials on the watersurface. Typical examples are oil slicks and floating debris. A similar situation occurs alsoduring the formation of sea ice, when small ice crystals (frazil ice) are mixed to form a verythin, soupy surface layer called grease ice. From here, solid ice begins to form as an agglomerateof disk-shaped ice blocks (the pancakes) floating on the grease ice layer [1].

All these situations tipically lead to wave attenuation [2], which is easily detectable throughremote sensing. Knowledge of the dispersion relation could then allow to determine the icecover properties [3].Effective mathematical models were developed in the case of water covered by simple viscouslayer [4, 5, 6, 7]. Such models however are no longer valid when floating impurities are present[8]. This prompted us to derive a dispersion relation for gravity waves in water covered by thindisk-like impurities, embedded in a viscous matrix. The derivation exploits standard techniquesin suspension theory. Wave damping and decrease of phase velocity is predicted in all cases.It is highlighted under which physical conditions and to what extent the disks modify theviscous layer model. It appears that the pancakes act mostly by changing the phase velocityof the waves (a sort of mass loading effect). On the contrary, in oil slicks , floating debris playa significant role also in modifying the wave attenuation.It must be stressed that these results are obtained within a dilute assumption (low surfacefraction of the disks). Some qualitative considerations on the close-packing limit are presentedthough, and the possible relevance of the results to real pancake ice discussed, providing acomparison with experimental data [8].

References

[1] V. A. Squire, et. Al, Ann. Rev. Fluid Mech.,1995, 27, 115-168.

[2] W. Alpers and H. Huhnerfuss, J. Geophys. Res., 1989, 94(C5), 6251-6265.

[3] P. Wadhams, et. Al., Geophys. Res. Lett., 2004, 31, L15305

69


[4] J. Weber, J. Phys. Oceanogr., 1987, 17, 2351[5] J. Keller, J. Geophys. Res., 1998, 103, 7663[6] R. Wang and H.H. Shen, J. Geophys. Res. , 2010, 115, C06024[7] G. De Carolis and D. Desiderio, Phys. Lett. A, 2002, 305, 399[8] R. Wang and H.H. Shen, Cold Reg. Sci. Technol., 2010, 61, 90

70


Intermittency in the Fractal Fourier Burgers Equation

Michele Buzzicotti, Luca Biferale, Uriel Frisch and Samriddhi Sankar RayDepartment of physics university of Rome Tor Vergata, 00133 Roma

We present theoretical and numerical results for the one-dimensional stochastically forcedBurgers equation decimated on a fractal Fourier set of dimension D. We investigate the ro-bustness of the energy transfer mechanism and of the small-scale statistical fluctuations bychanging D. We find that a very small percentage of mode-reduction (D . 1) is enough todestroy most of the characteristics of the original non-decimated equation. In particular, weobserve a suppression of intermittent fluctuations for D < 1 and a quasi-singular transition fromthe fully intermittent (D=1) to the non-intermittent case for D . 1. Our results indicate thatthe existence of strong localized structures (shocks) in the one-dimensional Burgers equation isthe result of highly entangled correlations amongst all Fourier modes.

71


Platelet margination in tubular blood flow

Timm KruegerMary Brück Building, King’s Buildings, University of Edinburgh, Edinburgh EH9 3DW Scotland, United

Kingdom

I will talk about platelet margination in tubular blood flow with a special emphasis on theeffects of tube diameter and the red blood cell capillary number Ca (i.e. the ratio of viscous fluidto elastic membrane forces). Platelet margination is important for blood clotting: the healingprocess of damaged blood vessel walls is initiated by nearby platelets. Platelets should thereforebe located close to the vessel wall, ideally within the layer that is free of red blood cells (cell-freelayer). The system is modelled as three-dimensional suspension of deformable red blood cellsand nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundaryand finite element methods.It turns out that a non-diffusive radial platelet transport facilitates margination. This non-diffusive effect is important near the edge of the cell-free layer, but only for Ca > 0.2, when redblood cells are tank-treading. Platelets at Ca > 0.2 eventually reach the cell-free layer wherethey are effectively captured. However, platelets can escape again for Ca < 0.2. Furthermore, Iwill talk about the platelet dynamics once they have reached the cell-free layer.

72


Regularised sourcelets and stokeslets for phoretic problems

Thomas Montenegro-Johnson, Sebastien Michelin and Eric LaugaDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for

Mathematical Sciences, Wilberforce Road, Cambridge, Cambridgeshire, UK

We present an efficient, accurate, flexible method for the solution of microscopic phoreticproblems at zero Peclet number. The method relies on successive solution of the Laplacian andthe Stokes flow equation using regularised Green’s functions with the boundary element method- for Stokes flow the well-known method of regularised stokeslets. The use of regularised Green’sfunctions allows for swift, simple numerical implementations. The boundary element method isparticularly suitable for phoretic problems, since no quantities in the domain bulk are requiredto solve the particle mobility; surface concentrations give the surface slip velocities, allowing theboundary traction calculation that yields particle velocities. Furthermore, the method requiresno re-triangulation for time-dependent problems, and simple boundaries such as a plane wallmay be added at no increase to the size of the linear system via the method of images.

73


Dynamics of flexible fibers in shear flows

M. L. Ekiel-Jezewska, A. M. Slowicka and E. WajnrybInstitute of Fundamental Technological Research, Polish Academy of Science, 02-106 Warsaw, Poland

Dynamics of a flexible non-Brownian fiber in a simple shear flow at the low-Reynolds-number is analyzed numerically for a wide range of the ratios A of the fiber bending force tothe hydrodynamic force. (Definition of the parameter A can be found in Slowicka,Wajnryb &Ekiel-Jezewska (2013).)A fiber is modeled as a chain of solid beads as in Gauger & Stark (2006). The centers ofthe consecutive beads are linked by springs with the equilibrium length so small that theconsecutive beads almost touch each other. The spring constant is so large that the fiber’slength practically does not change. At the equilibrium, the fiber is straight. At a deformedconfiguration, there appear a bending force exerted on each bead, proportional to the bendingparameter A.Time-dependent velocities of the beads are evaluated with the use of the Hydromultipolenumerical code, based on solving the Stokes equations by the multipole expansion, see Cichocki,Ekiel-Jezewska & Wajnryb (1999). The time-dependent positions of the beads are determinedby the adaptive fourth order Runge-Kutta method.Initially, the fiber is aligned with the flow, and the springs are at the equilibrium. Owingto symmetry, the centers of all the beads move in the plane perpendicular to the vorticitydirection. The fiber end-to-end vector tumbles, in a similar way as a rigid elongated body,see Jeffery (1922). While the fiber turns, its shape evolves accordingly, and the center-of-massoscillates across the flow.A surprisingly rich spectrum of different modes is observed when the value of A is systemati-cally changed, with bifurcations, period doubling and transition to chaos (For the details, seeSlowicka,Wajnryb & Ekiel-Jezewska (2015).)For a range of very small and a range of large values of A, the center-of-mass trajectories areperiodic with a single tumbling time τ , and there is no migration across the flow. For smallvalues of A, the center-of-mass trajectories are regular, but consecutive tumbling times differfrom each other, what leads to migration. For moderate values of A, a chaotic behavior isobserved - a large sensitivity to a small change of A with (typically) many irregular values ofτ or (exceptionally) a regular migration.

74


At a moderate value of A, a transition is observed between the straightening out mode of morestiff fibers to the coiled mode of more flexible fibers. In the straightening out mode, the fibersignificantly changes its shape while tumbling - from almost straight and aligned with the flowto S-shaped. In the coiled mode, the fiber is always compact, it never straightens out.

ReferencesCichocki, B., Ekiel-Jezewska, M. L. & Wajnryb, E. 1999 J. Chem. Phys. 111, 3265.Gauger, E. & Stark, H. 2006 Phys. Rev. E 74, 021907.Jeffery, G. 1922 Proc. R. Soc. Lond. A. 102, 161-179.Slowicka, A. M., Wajnryb, E. & Ekiel-Jezewska, M. L. 2013 Eur. Phys. J. E 36, 1-12.Slowicka, A. M., Wajnryb, E. & Ekiel-Jezewska, M. L. 2015 2015 J. Chem. Phys.143, 124904..

75


Purely-elastic flow instabilities in a microfluidic flow

focusing device

Pierre Ballesta and Manuel A. AlvesFaculdade Engenharia Universidade Porto, Dep. Engenharia Quimica, Rua Dr. Roberto Frias, 4200-465

Porto,Portugal

We studied the behaviour of dilute and semi-dilute polymer solutions flowing in a microflu-idic flow-focusing device, where two balanced lateral streams stretch an inlet stream. The re-sulting velocity field is investigated using time-resolved micro particle imaging velocimetry. Byvarying the flow rates in the inlet and lateral channels and their ratio, we observed several typesof flow transitions and analysed the resulting velocity field both upstream and downstream ofthe cross section. Eventually, at high flow rates, the flow becomes chaotic. Moreover the pathto a chaotic state depends on both the flow rates and the flow rate ration between the lateraland central channels.

76


Head-on collision between two spherical chemically active

particles

Z. Eskandari, M. N. Popescu, M. Tasinkevych, and S. DietrichMax Planck Institute for Intelligent Systems, Heisenbergstrasse 3,70569 Stuttgart, Germany

A spherical micron-sized particle with catalytically active coating on art of its surface canmove within a liquid solution by promoting chemical reactions in the solution. This producesgradients of chemical species around the surface of the particle, which gives rise to a "phoretic"slip due to interaction (attraction or repulsion) of the chemical solute with the surface of theparticle. When two such active particles approach each other, the distributions of solutes inthe vicinity of the particles overlap, which gives rise to effective interactions in addition tothe purely hydrodynamic ones. Thus these particles effectively interact via a complex couplingbetween hydrodynamics and distribution of solute particles.Here, we study numerically the binary collision of two identical chemically active particlesfocusing, in the first instance, on the case of head-on collision and a single solute species. Wepresent and discuss the outcome of such collisions as a function of the catalyst coverage, therelative orientation (parallel or antiparallel particle directors), and the repulsive or attractivecharacter of the solute-particle interaction. For catalyst coverages above a certain thresholdand repulsive interaction, we find that stable steady states emerge in which the self-propellingmotion is balanced by the hydrodynamic repulsion. When changing the interaction between thesolute and the surface of the particles from repulsion to attraction, steady states are no longerfound irrespective of the coverage of catalyst.Finally, by "clamping" the phoretic slip around the particle to the distribution correspondingto a particle in the bulk, we obtain the case of binary collisions between "squirmers". Thedifferences between these and the collisions of the self-phoretic particles allow us to isolatecontributions arising solely from the changes in the distribution of phoretic slip with the inter-particle separation.

77


Multiscale Modeling of Transport in Confined Media

M. Göktug AhunbayIstanbul Teknik Universitesi, Kimya Mühendisligi Bölümü Ayazaga Kampusu, 34469, Maslak, Istanbul, Turkey

Fluid flow in confined media, such as membranes for water treatment, nanoporous mate-rials for adsorptive separation of gas mixtures, ionic liquids in porous carbon electrodes forsupercapacitors involves length and time scales spanning several orders of magnitude from theatomistic level to the continuum level. From the modelling point of view, the challenge posed bythese multiple scales is to integrate these different scales, in order to obtain a thorough analysisof the transport phenomenon. Here, multiscale modeling and simulation approaches to addressthese type of problems will be reviewed.

78


Digital Fourier Microscopy: a versatile tool for complex

dynamics

Fabio Giavazzi, Roberto CerbinoUniversitá degli Studi di Milano, Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, 20090

Segrate (MI), Italy

Optical microscopy is routinely used for the investigation of a large number of systems ofinterest in physics, material science and biology: by probing the sample directly in the realspace it provides a unique, straightforward, access to its local properties. In the past yearsthere has been a growing interest in methods aimed at extracting from the microscopy imagesa quantitative information on the structure and the dynamics of the sample, even in fields,like cell biology, where microscopy is traditionally considered and used as a qualitative orsemi-quantitative tool. Methods like Single Particle Tracking and Particle Image Velocimetry,are now routinely used in a variety of contexts and are part of the basic toolbox of manymicroscopists.Recently, a conceptually different approach has been proposed, known as Digital FourierMicroscopy (DFM) which is based on the characterization of the correlation properties of thesample in the reciprocal space via spatial Fourier analysis of the images [1, 2]. At a variancewith the previously mentioned methods, typically relying on the direct identification of probeparticles or on the measurement of the local properties of a flow field, a DFM techniquecan provide a reliable quantitative information even when the particles are well below thediffraction limit and in extreme conditions of low signal-to-noise ratio.In this contribution we illustrate the potential of DFM in providing a robust and compactcharacterisation of microsystems by presenting in detail two very different case studies: thedynamics of stress-driven plastic rearrangements in a coarsening foam and the collectivemigration patterns in confluent epithelial cell monolayers.

References[1] R. Cerbino and V. Trappe Phys. Rev. Lett. 100188102 (2008)[2] F. Giavazzi and R. Cerbino, J. Opt.16 083001 (2014)

79


2D and 3D Migration and Proliferation of Cells and

Cellular Tissues by Time-Lapse Microscopy and Image

Analysis: a Transport Phenomena approach to Active

Bio-Soft-Matter

Flora Ascione, Sergio Caserta, Stefano GuidoUniversitá degli studi di Napoli Federico II, Dipartimento di Ingegneria Chimica dei Materiali e della

Produzione Industriale, 80128 Napoli Italy

Many physiological and pathological processes, such as inflammation, tissue repair, angio-genesis, tumour growth and invasion, are strongly linked to the dynamic evolution of activebiological soft mattes. The current understanding of many mechanisms is still limited and celldynamic behavior remains a challenging process to study under physiopathologically-relevantconditions in vitro. A detailed analysis of these processes requires a rigorous approach to quan-titatively analyze cell dynamics and measure cell movement and proliferation indices. This workis addressed to investigate the dynamic evolution of biological soft matter, from single to col-lective cell dynamic behavior in 2D and 3D substrata, in a quantitative way. The methodologyis based on direct visualization of cell migration assays by live cell imaging using in-vitro TimeLapse microscopy, analyzed using image analysis. The technique is based on iterative imageacquisition within the sample by means of a motorized video-microscope that is kept in a con-trolled environment to ensure cell viability thanks to an incubating system.Different assays, such as single cell random motility assays or Wound Healing assay were usedto gain quantitative information about the movement of individual cells, and cell populations,such as cell monolayers or clusters in 2D and 3D. The response of individual cells and groupsof cells to the concentration gradient of a chemoattractant was also investigated by using achemotactic chamber.The experimental data were interpreted according to mathematical models, based on a trans-port phenomena approach.

80


Angular Dynamics of a spheroid in shear at small

Reynolds number

Einarsson, Candelier, Lundell, Angilella, MehligDepartment of Physics, University of Gothenburg, 41296 Gothenburg, Sweden

I describe an effective equation of motion for the angular dynamics of a neutrally buoyantspheroid suspended in a simple shear flow, valid for arbitrary particle aspect ratios and to linearorder in the shear Reynolds number. We show how inertial effects lift the degeneracy of theJeffery orbits at small shear Reynolds numbers. For prolate spheroids tumbling in the shearplane is stable, log-rolling is unstable. For oblate spheroids, by contrast, log-rolling is stable andtumbling is unstable provided that the particle is not too disk-like. For disks both log-rollingand tumbling are stable, separated by an unstable limit cycle.

81


Lattice Boltzmann approach to liquid - vapour separation

T. Biciusca, A. Cristea, A. Lamura, G. Gonnella, V. SofoneaCenter for Fundamental and Advanced Technical Research Romanian Academy, R - 300223

Timisoara,Romania

A two-dimensional lattice boltzmann model is used to investigate various problems relatedto liquid - vapor separation: the bubble cavitation problem in quiescent and sheared fluids, theRayleigh-Plesset equation and the morphology of phase separation in gravitational field.

82


Quantifying the role of turbulence on droplet growth by

condensation

G. Sardina, F. Picano, L. Brandt, R. CaballeroDepartment of Meteorology, Stockholm University, 106 91 Stockholm,Sweden

We quantify the impact of turbulence on the process of condensation/evaporation of waterdroplets suspended inside warm clouds. A spectacular droplet growth by condensation andcoalescence (about four decades in size) is observed in warm clouds in relatively short times(even less than half an hour), something which we cannot yet understand and predict. Therole of turbulence on this process is still debated. While the effects of turbulence on collisiondynamics has been recently addressed, little is known about the effects on condensation. Wepresent a stochastic model able to predict the droplet growth by condensation in real clouds. Themodel is validated and supported by Direct Numerical Simulations (DNS) reproducing dropletcondensation over time intervals of 20 minutes, comparable with the time of rain formation. Weshow that the variance of the droplet size increases in time as t1/2, with a growth dependent onthe large to small turbulent scale separation, and independent of the turbulence smallest-scales.The present results demonstrate that every warm cloud will precipitate given a sufficiently long"life" time.

83


Microrheology in a hard-sphere colloidal glass: Simulations

and Theory

Markus Gruber, Antonio M. Puertas, Gustavo Abade, Thomas Voigtmann, Matthias FuchsDepartamento de Quimica y Fisica, Universidad de Almeria, 04120 Almeria,SPAIN

We compile in this presentation results of simulations and mode-coupling theory of activemicrorheology in dense colloids, beyond the glass transition: a single tracer is pushed with aconstant force through the system. In the simulations, quasi-hard particles follow Langevindynamics, and the tracer trajectory is monitored, to obtain the friction coefficient, correlationfunctions, van Hove functions, and other dynamical observables. The theoretical model is basedon the mode-coupling theory for the glass transition and provides specific predictions that aretested against the simulations, with very good agreement.

At small forces, the tracer is localized and cannot break free. The complex tracer positioncorrelation functions decay to a plateau, so called non-ergodicty parameter, which is correctlygiven by the theory. The van Hove functions, or tracer position distribution function, show anexponential tail, extending to several particle diameters in the force direction, and shorter inthe transversal direction, in addition to a Gaussian maximum at small distances.

When the tracer is pushed with a large force, on the other hand, it can break free showingsuperdiffusion in the force direction, absent in the theory, with an exponent of approximately1.6-1.7. The friction coefficient can be calculated from the steady velocity at long times, de-creasing with increasing external force.

84


Controlled generation of topological defects in nematic

microfluidical environment

Ziga Kos, Miha RavnikFaculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia

Recent advances in microfluidics show promising results in biomedicine, material science,and other related fields. Due to their miniaturization, microfluidical devices are often utilizedin a lab-on-a-chip concept. Their versatility is further increased by introducing an anisotropicfluid, such as nematic liquid crystal, in the microfluidical matrix, showing great potential inoptics, sensing, material synthesis, and transport. A control of nematic defects in a microfluidicalenvironment is necessary to fully utilize potential applications.

We have applied hybrid lattice-Boltzmann simulations to model the behavior of nematicnear the junctions of microchannels. Depending on the flow direction in the channels, such mi-crofluidical platform can be used to induce nematic topological defects with different topologicalcharges. In particular, the defects in the nematic field are coupled with the velocity field. Wetest different geometries of the junctions and contact points, and the role of surface anchoring.Furthermore, the nematic configuration at the junction can be controlled by the input/outputvelocity. Finally, the work is a contribution towards topological microfluidics of complex fluids.

85


Effects of composition, water plasticization and

pre-crystallization process on the flowability of model

dairy powders

Runjing Li1,2, Yrjö H. Roos2, Song Miao11 Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland

2 School of Food and Nutritional Sciences, University College Cork, Cork, Ireland

The flow properties of spray-dried dairy solids depend on their composition, physical char-acteristics and process conditions. This study investigated the influence of water plasticization;lactose content and pre-crystallization process on flow properties of lactose/milk protein iso-late (MPI) solids systems. Mechanical study showed that the higher was the lactose contentin dairy solids, the more significant was the change in their modulus at glass transition re-gion. Lactose/MPI mixtures with higher lactose contents showed better flowability, but theygave bigger friction angles after storage at same relative humidity. Morphological characteris-tics study indicated dairy solids with higher crystallinity had less rounded shape and roughersurface. Increasing protein content or crystalline lactose content could decrease the molecularmobility of dairy solids. Flow function tests indicated that dairy solid with 11.1% crystallinitywas more easy-flowing than lactose/WPI mixtures with 1.0%, 29.2% and 46.8% crystallintiy at0% and 44% relative humidity (RH) storage conditions. Furthermore, dairy solids with higheramount of crystalline lactose showed better resistance to develop cohesive at high RH storageconditions.

86


Active particles at and close to fluid-fluid interfaces

Paolo Malgaretti 1,2, Mihail Popescu 1,2, Alvaro Dominguez 3, Siegfried Dietrich 1,2

1Max-Planck-Institut fur Intelligente Systeme, Stuttgart, Germany2IV. Institut fur Theoretische Physik, Universitat Stuttgart, Germany

3Departamento de Física Teórica, Universidad de Sevilla, Sevilla, Spain

Chemically active swimmers are particles whose surface promotes the catalysis of suspendedmolecules. When the surface properties of these particles are not homogenous, the asymmetryin the density field generated by the process of catalysis can lead to particle motion [1,2].In this contribution I will discuss how the presence of a fluid-fluid interface affects the dynamicsof chemically active particles. In particular I will focus on two main cases, namely the case inwhich active particles are already trapped at the interface and the case in which they are close(but not yet trapped) to a fluid-fluid interface.When the particles are trapped at fluid-fluid interfaces their motion is constrained along thedirection parallel to the interface. In such a scenario, the presence of a viscosity contrastgenerates torques on the particle promoting states for which the torque disappear (not motilestates) or it is balanced by the interface (motile states) [3].In the case in which active particles are suspended close to a fluid-fluid interface, the densityfield they generate will be distorted by the interface hence leading to the onset of additionalgradients both perpendicular and parallel to the interface. In this scenario, if the byproducts ofthe catalysis are surface active, their inhomogeneous distribution at the interface will affect thelocal surface tension hence setting up Marangoni flows. I will show, via a simplified model, howsuch Marangoni flows arise and how they can attract (repel) the particle from the interface.Finally I will briefly discuss collective effects [4].

References1. R. Golestanian, T. B. Liverpool and A. Ajdari, Phys. Rev. Lett., 94, 220801 (2005).2. R. Kapral, J. Chem. Phys., 138, 020901 (20013).3. P. Malgaretti, M.N. Popescu and S. Dietrich In preparation.4. A. Dominguez, P. Malgaretti, M.N. Popescu and S. Dietrich Phys. Rev. Lett. in press.

87


Copepod acceleration: statistical analysis from high speed

camera measurements

F.G. Schmitt, I. Benkeddad, S. Souissi, H. Ardeshiri, E. CalzavariniCNRS, Laboratory of Oceanology and Geosciences, 28 avenue Foch, 62930 Wimereux, France

Since the years 1980, it was observed that calanoid copepods were able to perform, usingtheir antennas and other appendices, jumps at a high speed. This is the result of an adaptationto a very fluctuant and turbulent medium, after many generations. This provides also copepodssome abilities to reach very large acceleration values, in order to escape from predators.

In this study, females and males of the species Eurytemora affinis and Acartia tonsa werefilmed in an aquarium using a high speed camera, in order to extract trajectories, velocities andaccelerations. Recording were done at a frequency of 1000 frames/second, and the movementsstimulated using two diods situated on both sides of the aquarium, and lightened successivelyto obtain moves by phototropism. We found that the swimming of these copepods was done bysuccessive jumps corresponding to large velocities during a very brief time, associated with verystrong acceleration events, during typically a time of the order of 15 ms. In this comparativestudy, we were interested in the possible influence of the species, the genre and the size on theswimming statistics. The mean peak accelerations of the species E. affinis are around 15 G,whereas for the species A. tonsa the values were slightly larger (18 G). The statistics of thejump duration, time between jumps, velocity and acceleration dynamics during jump events,are considered for both species.

88


Pedestrian dynamics: accurate data collection and

modeling

Chung-min Lee1, Alessandro Corbetta2, Roberto Benzi3, Adrian Muntean4, Federico Toschi21California State University Long Beach, Long Beach, CA, USA

2Eindhoven University of Technology, Eindhoven, The Netherlands3University of Rome, Tor Vergata, Rome, Italya

4Karlstad University, Karlstad, Sweden

Pedestrian dynamics modeling is critical for civil infrastructure design. To achieve quantita-tive understanding, high statistics and high quality real life data is essential. We used MicrosoftKinect 3D-range sensors for more than 100 working days to record pedestrian movements 24/7in a corridor in a building at Eindhoven University of Technology. Together with automatic headtracking techniques we collected few hundreds of pedestrian trajectories with exceptionally highspace and time resolutions. Based on the observed statistics we drew an analogy between pedes-trians and active Brownian particles and constructed a generalized Langevin model that takesinto account the geometric restrictions of the corridor, pedestrians’ destination and turning-back events. The model is shown to quantitatively reproduce the observed single pedestrianwalking patterns as well as the statistics of ordinary and rare fluctuations. Furthermore, themodel can be expanded to describe multi-pedestrian dynamics.

89


Pedestrian dynamics: from pairwise interactions to large

scale measurements

Alessandro Corbetta1, Chung-min Lee2, Roberto Benzi3, Adrian Muntean4, Federico Toschi11Eindhoven University of Technology, Eindhoven, The Netherlands2California State University Long Beach, Long Beach, CA, USA

3University of Rome, Tor Vergata, Rome, Italy4Karlstad University, Karlstad, Sweden

The dynamics of pedestrian crowds shares deep connections with statistical physics and fluiddynamics. From an applied perspective, understanding these dynamics is a paramount step toensure a safe and serviceable built environment. Employing our high statistics experimental datacollected in real-life conditions in a corridor at Eindhoven University of Technology, we measurethe avoidance force between pairs of pedestrians. On this basis, we extend a Langevin model forthe undisturbed dynamics to include pairwise "social" interactions. To broaden our study, weperformed continuous recordings of walking pedestrians within Eindhoven Train Station. In a sixmonths-long experimental campaign we collected massive data for resolved statistic descriptionsof the dynamics. We showcase preliminary analyses and related investigation techniques.

90


Adhesion strengths, shapes and the dynamics of red blood

cell clusters at stasis and in microcapillary flow

Christian WagnerSaarland University, Experimental Physics, 66123, Saarbruecken, Germany

Cell migration and flow through the vascular network is mostly determined by bloods ma-jority component, the red blood cells (RBC«s). RBC«s at stasis have the tendency to formlarge aggregates, the so called rouleaux. They are induced by the plasma proteins such as fib-rinogen but can be reversibly broken up in the non-equilibrium situation of a shear flow. Thisis the physical origin of the pronounced shear thinning of blood. The addition of syntheticmacromolecules such as dextran to a physiological solution containing RBC«s can mimic theformation of rouleaux.We use single cell force spectroscopy to characterize typical adhesion energies, both for dextranand fibrinogen, and we use confocal microscopy and numerical simulations to study the topol-ogy of these aggregates as a function of the adhesion energy. Our in vitro, in vivo and numericalstudies show that despite large shear rates, the presence of either fibrinogen or the syntheticpolymer dextran leads to an enhanced formation of robust clusters of RBC«s in microcapillar-ies under flow conditions. However, the contribution of hydrodynamic interactions comparedto the interactions induced by the presence of macromolecules in the cluster formation has notbeen established. Here we compare hydrodynamical cluster formation of RBC«s and clusterformation of RBC«s in the presence of macromolecules in microfluidic flow. The results revealstrong differences in the cluster morphology. The surface-to-surface distance between cells inthe different solutions shows a bimodal distribution that can be reproduced with our numericalsimulations by varying the bending rigidity of the cell membrane within the tabulated rangereported in healthy physiological conditions.

91


Anomalous transport of circular swimmers in disordered

structures: classical edge-state percolation

Thomas FranoschInstitut für Theoretische Physik, Universität Innsbruck, Innsbruck, Austria

Recently micron-sized self-propelled particles have been realized as model systems [1] forcomplex living organisms such as bacteria. If the agent is asymmetric a natural circular motion[2] emerges which yields characteristic skipping orbits when interacting with boundaries. Here,we investigate by molecular dynamics simulations the dynamics of circular swimmers in atwo-dimensional model with randomly distributed scatterers. For small radii of the swimmingmotion the agents orbit only around isolated clusters of scatterers, while at large radii diffusivebehavior emerges. A de-localization transition occurs which is generated by percolatingskipping orbits along the edges of obstacle clusters. Directly at the transition the mean-squaredisplacements displays subdiffusive transport. The dynamic exponents differ from those ofthe conventional transport problem on percolating systems, thus establishing a new dynamicuniversality class [3]. Last, we draw an analogy to the field-induced localization transition inmagnetotransport in 2D electron gases in a disordered array of antidots.

[1] F. Kümmel, Borge ten Hagen, Raphael Wittkowski, Ivo Buttinoni, Ralf Eichhorn, Gio-vanni Volpe, Hartmut Löwen, and Clemens Bechinger Phys. Rev. Lett. 110, 198302 (2013).

[2] S. van Teeffelen and H. Löwen, Phys. Rev. E 78, 020101(R) (2008).[3] W. Schirmacher, B. Fuchs, F. Höfling, and T. Franosch, Phys. Rev. Lett. 115, 240602

(2015).

92


Robust Energy Transfer Mechanism via Precession

Resonance in Nonlinear Turbulent Wave Systems

Brendan Murray and Miguel D.BustamanteSchool of Mathematics and Statistics, University College Dublin, Belfield, Dublin 4, IRELAND

The study of energy exchanges taking place within nonlinear wave systems has relevance forgeophysical flows, oceanic waves, nuclear fusion devices and nonlinear optics. Certain efficienttransfers are manifest as extreme events, localised in space and time, and help determine thedynamics of turbulent cascades across the spatial scales within such systems.

The precise mechanisms by which energy is most efficiently transferred in a turbulent systemremain an important open question. In this work we present a newly discovered resonance whichis found to drive transfers across the spectrum of Fourier modes in a nonlinear wave system.Quadratic nonlinearity of the governing PDE results in modes interacting in triads and, byexamining the precessional frequencies of the triad phases, we show transfers are maximal whenphase precession frequencies resonate with the nonlinear oscillation frequencies. This can leadto a collective state of synchronised triads with intense cascades at intermediate nonlinearity.

The Charney-Hasegawa-Mima (CHM) equation is a nonlinear dispersive wave system with aquadratic nonlinearity that underpins this phase precession resonance mechanism. It describesthe leading order, large scale dynamics of an incompressible, shallow layer of fluid on a rotatingsphere under the beta-plane approximation. By introducing a background vorticity it admitsthe existence of plane wave solutions, called Rossby or drift waves. Rossby waves are importantin determining the large scale evolution of geophysical flows, exerting influence over the atmo-spheric circulation between different regions and the formation of global circulation patternswhich are vital to weather forecasting and climate modelling.

For the CHM equation in 2-D, results are presented for a heavily truncated 4-mode, 2-triad system where we find that the phase precession resonance mechanism is driven by theunstable manifolds of periodic orbits embedded in the state space. This energy transfer isexposed through a systematic sampling of the system’s initial energy, which allows us to locateexplicitly some of these periodic orbits and examine their trajectories with respect to theefficiency of the energy transfer. Finally, results from this small-scale model are expanded tosystems of many degrees of freedom, where we uncover the correlations between phase precessionfrequencies and Fourier mode amplitudes.

93


Emplacement of the lavaflow of Bardarbunga Iceland

Armann Höskuldsson, Thor Thordarson and Ingibjorg JonsdottirInstitute of Earth Sciences, University of Iceland Sturlugata 7, 101 Reykjavik, Iceland

The Bardarbunga eruption began on 31 of August 2014 and lasted for 6 months. Duringthis time a high temperature lava was emplaced on a relative flat ground. Due to that detailedmeasurements of the extension of the lava could be done several times per day. In this presen-tation we shall compare the natural emplacement of the lava flow and theoretical calculations.Try to identify the main difficulties in modeling active lava flows that constantly change thefluid physics as it flows.

94


Non-Newtonian transport properties of granular

suspensions under simple shear flow

V. Garzó, M. G. Chamorro and F. Vega ReyesDepartamento de Fisica, Universidad de Extremadura, Avenida de Elvas sn, 06006-Badajoz (Spain)

Non-Newtonian transport properties in a steady simple shear flow state of a gas-solidsuspension at low-density are studied. The solid particles are modeled as a gas of smoothhard spheres with inelastic collisions while the influence of the surrounding interstitial fluid onthe dynamics of grains is modeled by means of a volume drag force [1]. The model is solvedby using three different but complementary routes, two of them theoretical (Grad’s momentmethod applied to the Boltzmann equation and an exact solution of a kinetic model adaptedto granular suspensions) and the other being computational (Monte Carlo simulations of theBoltzmann equation). In contrast to previous studies on granular sheared suspensions [2], thecollisional moment associated with the momentum transfer is determined in Grad’s solutionby including all the quadratic terms in the stress tensor. This theoretical enhancement allowsus for the detection and evaluation of the normal stress differences in the plane normal to thelaminar flow. In addition, the exact solution of the kinetic model gives the explicit form of thevelocity distribution function and its corresponding velocity moments. Comparison betweenour theoretical and numerical results shows in general a good agreement for the non-Newtonianrheological properties, the kurtosis (fourth velocity moment of the distribution function) andthe velocity distribution of the kinetic model for quite strong inelasticity and not too largevalues of the (scaled) friction coefficient characterizing the viscous drag force [3]. This showsthe accuracy of our analytical results that allows us to describe in detail the flow dynamics ofthe granular sheared suspension.

[1] V. Garzó, S. Tenneti, S. Subramaniam, and C. M. Hrenya, J. Fluid Mech. 712, 129(2012).

[2] A. S. Sangani, G. Mo, H.-K. Tsao, and D. L. Koch, J. Fluid Mech. 313, 309 (1996).[3] M. G. Chamorro, F. Vega Reyes and V. Garzó, Phys. Rev. E 92, 052202 (2015).

95


Self-organized active agents in a fluid environment:

hydrodynamics matters

Alessandro De Rosis, Emmanuel Leveque, Stefano Ubertini, Sauro SucciEcole Centrale de Lyon - Laboratoire de Mecanique des Fluides et d’Acoustique, 36 avenue Guy de Collongue,

69134, Ecully, France

We study self-organized living groups of active agents moving in a fluid environment. Theproposed solution strategy combines behavioral and hydrodynamic aspects. In particular, themutual interaction between the agents is described by solving the collective behavioral equa-tions. On the other hand, individuals are idealized as solid bodies immersed in a viscous fluidwhich, in turns, exerts an influence on the motion. The lattice Boltzmann and Immersed bound-ary methods are employed from the purely hydrodynamic side, thus allowing us to computethe fluid forces. Then, the position of the group is updated by integrating in time the equationof the solid motion. We use this strategy to evaluate the persuasive performance of an aspirantleader that is inserted among the group and it is forced along a prescribed path. Numericalsimulations are carried out by varying the size of the group and the Reynolds number. To esti-mate the leader’s performance, considerations about the compactness of the group are carriedout in terms of subpartitioning. A marked influence of the fluid environment clearly appears.

96


Translational and rotational temperatures of a granular

impurity in a gas of inelastic rough particles in the

homogeneous cooling state

F. Vega Reyes, V. Garzó and A. SantosDepartamento de Fisica, Universidad de Extremadura, Avda. Elvas s/n, 06071 Badajoz, Spain

We study in this work the properties of the homogeneous cooling state (HCS) of a granularimpurity immersed in a low density (dilute limit) gas of inelastic rough hard spheres. Wemodel statistically the granular impurity via the inelastic Boltzmann-Lorentz kinetic equationand the granular gas via the inelastic Boltz- mann equation. It can be proved that, after agenerally short transient time (that depends on the degree of roughness and inelasticity inthe collisions), the granular gas of rough particles and the impurity always reach a normalstate that, in the appropriate dimensionless representation, is formally stationary. We solvethe corresponding kinetic equation for steady states by means of two independent approaches:a) an analytical solution (using a multi-temperature Maxwellian approximation) of the kineticequation, thus obtaining expressions in the steady state; b) an exact numerical solution,computed with the direct simulation Monte Carlo method (DSMC). With the aid of bothmethods, we describe the general properties of the translational and rotational temperaturesof the impurity in the HCS.

Acknowledgements This work is supported by the Ministerio de Educacion y Ciencia (Spain)through Grant No. FIS2013-42840-P and through Grant no. GR15104 (partially financed bythe European Regional Development Fund, ERDF).

97


Flow of interacting colloidal suspensions through a narrow

channel

S. Arietaleaniz, I. Pagonabarraga and R.C. HidalgoDepartment of Applied Physics and Mathematics, Edificio de los Castaños. C/Irunlarrea s/n, Universidad de

Navarra, 31080 Pamplona (Navarra)

In this work, the constitutive responses of colloidal suspensions at intermediate and highconcentrations are studied. We examine the role of the interaction potential on a suspension,flowing through a narrow channel at low Reynold’s numbers. We perfume simulations of con-fined colloidal suspensions between two parallel plates using Lattice Boltzmann; analyzing therheological response of the suspension, once the steady state is established. In those conditions,we explore the impact that the range and strength of the inter-particle potential has on thefluid mechanical response. For dilute suspensions, we always recover a Newtonian behavior.At higher volume fractions, the range of the potential has a stronger impact in the behav-ior of the suspension. While for short range potentials the non-Newtonian response is mostlydependent on colloid concentration, for a Lennard-Jones potential we identify two rheologicalresponses depending on the potential strength, ξLJ , at a given concentration. For weak ξLJ ,the effective viscosity, ηeff decreases as a function of ξLJ until a minimum is reached. On thecontrary, at large values of ξLJ the effective viscosity ηeff increases when increasing the strengthof interaction. This behavior has been correlated with the local structure of the fluid.

98


Self-assembly of colloidal bands driven by a periodic

external field

André S. Nunes, Nuno A. M. Araújo, Margarida M. Telo da GamaCentro de Física Teórica e Computacional, Faculdade de Ciências da Universidade de Lisboa, Campo Grande,

Ed-C8, 1749-016 Lisboa

We study the formation of bands of colloidal particles driven by periodic external fields.Using Brownian dynamics, we determine the dependence of the band width on the strength ofthe particle interactions and on the intensity and periodicity of the field. We also investigate theswitching (field-on) dynamics and the relaxation times as a function of the system parameters.The observed scaling relations were analyzed using a simple dynamic density-functional theoryof fluids.

99


Flow visualization of a particulate blood analogue

reproducing the erythrocytes cell free layer

Diana Pinho1,2, Laura Campo-Deaño2, Rui Lima3, Fernando Pinho21ESTiG, Polytechnic Institute of Bragança, 5301-857, Bragança, Portugal

2CEFT, DEMec, Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal3Mechanical Engineering Department, University of Minho, Campus de Azurém, 4800-058 Guimarães,

Portugal

Interest on the development of rheological and physiological blood analogues has beenincreasing as a consequence of the increasing amounts of experimental hemodynamic researchand the difficulties associated with the manipulation of real blood in vitro because of ethical,economical and hazardous issues.Blood exhibits complex flow behaviour due to the presence of proteins and suspended cellularelements in plasma, such as platelets, leucocytes and mainly erythrocytes (red blood cells,RBC). Under normal flow conditions blood flow is strongly influenced by the interaction of theRBCs with the vessel walls and the surrounding medium. It is well known that when bloodflows through narrow vessels a cell-free plasma layer forms near the wall. The formation of thisplasma-rich layer is well documented in the literature on microchannels with diameters lessthan 300 µm [1,2]. Different Newtonian and non-Newtonian [3] blood analogues, able to mimicthe rheological properties of real blood have been developed. However, none of them is ableto mimic simultaneously both the rheological behaviour and the physiological response of theRBCs, i.e. the formation of cell-free plasma layer around the walls. In this work we present aviscoelastic suspension of spherical particles, made of xantham gum and dextran, which is ableto mimic the rheological response of human RBCs in dextran, when this fluid flows througha 100 µm glass capillary and a hyperbolic microchannel. Rheological measurements of theblood analogues were performed under steady shear flow conditions and the flow visualizationsthrough a 100 µm glass capillary and through the hyperbolic microcontractions were carriedout to observe the formation of plasma layer by the blood analogues and then compared withplasma layers formed in real blood flows.

AcknowledgmentsThe authors acknowledge the financial support provided by Fundação para a Ciência e a

100


Tecnologia (FCT), COMPETE and FEDER through projects PTDC/SAU-BEB/105650/2008,PTDC/SAU-ENB/116929/2010, PTDC/EQUFTT/118716/2010, EXPL/EMS-SIS/2215/2013,fellowships SFRH/BD/89077/2012, and grant IF/00148/2013.

References[1] Lima, R. et al. Single and two-phase flows on chemical and biomedical engineering. Dias,

R., Martins, A. A., Lima, R., Mata, T. M. 8eds) Bentham Science Publishers: Netherlands,513-547, 2012

[2] Garcia, V.,et al., Applied Biological Engineering - Principles and Practice, Ganesh R.Naik (ed.), InTech, Vol. 17, 394-416, 012.

[3] Campo-Deaño, L., et al., Viscoelasticity of blood and viscoelastic blood analogues foruse in polydymethylsiloxane in vitro models of the circulatory system, Biomicrofluidics, 7,034102, 2013.

101


Manipulation of long-term dynamics in a colloidal active

matter system using speckle light fields

Erçag Pinçe, KPV Sabareesh, Agnese Callegari, Parviz Elahi, Sylvain Gigan, Giovanni Volpeand Giorgio Volpe

Department of Physics, Bilkent University, Çankaya, Ankara 06800, Turkey

Particles undergoing a stochastic motion within a disordered medium is a ubiquitous phys-ical and biological phenomena. Examples can be given from organelles performing tasks in thecytoplasm to large animals moving in patchy environment. Here, we use speckle light fields tostudy the anomalous diffusion in an active matter system consisting of micron-sized silica par-ticles (diameter 5 µm) and motile bacterial cells (E. coli). The speckle light fields are generatedby mode mixing inside a multimode optical fiber where a small amount of incident laser poweris needed to obtain an effective disordered optical landscape for the purpose of optical manipu-lation. We experimentally show how complex potentials contribute to the long-term dynamicsof the active matter system and observed an enhanced diffusion of particles interacting withthe active bacterial bath in the speckle light fields. We showed that this effect can be tunedand controlled by varying the intensity and the statistical properties of the speckle pattern.Potentially, these results could be of interest for many technological applications, such as themanipulation of microparticles inside optically disordered media of biological interest.

102


A new microfluidic methodology to assess the

haemocompatibility of magnetic nanoparticles designed for

theranostic applications

R.O. Rodrigues1,2, M. Bañobre-López3, J. Gallo3, P.B. Tavares4, A.M.T. Silva2, H.T. Gomes1

and R. Lima51LSRE-LCM, Polytechnic Institute of Bragança, Campus de Santa Apolónia, 5300-857 Bragança, Portugal2 LSRE-LCM, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto,

Portugal3 INL - International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga, 4715-330 Braga, Portugal4CQVR - Centro de Química, Universidade de Trás-os-Montes e Alto Douro, 5000-801 Vila Real, Portugal5 University of Minho, Department of Mechanical Engineering, Campus de Azurém, 4800-058 Guimarães,

Portugal / CEFT - Centro de Estudos de Fenómenos de Transporte, Faculdade de Engenharia da

Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

The remarkable physicochemical properties of magnetic nanoparticles (MNPs) at thenanoscale have boosted the development of new and promising strategies for the simultaneousdiagnosis and treatment of diseases, particularly in cancer therapy Ð the so-called theranosticapplications (1). In these strategies, the intrinsic superparamagnetic properties of MNPs havebeen exploited to gain access into multifunctional systems able to simultaneously performas enhanced magnetic resonance imaging (MRI) contrast agents, efficient nanocarriers fordrug delivery and nanoheaters in magnetic hyperthermia based therapy (2), among others.Nevertheless, the lack of biocompatibility and haemodynamic studies, hamper the consoli-dation of the multifunctional nanoparticles as the next generation of therapeutic bio-agentsin medicine. In order to gain deeper insight into the complex nanoparticle-red blood cells(RBCs) membrane interaction, a novel microfluidic methodology was developed based on thehuman RBCs deformability as an indicator of haematological pathologies and disorders (3).For this purpose, a microfluidic device with a hyperbolic channel based on the extensionalflow approach and a high-speed video microscopy system was used. The microfluidic flowresults revealed the higher accuracy of the novel presented methodology compared to thetraditional tests (haemolysis analysis), since smaller increments in the rigidity of the RBCs canbe detected. The rigidity alterations have been reported to be due to the wrapping of smallMNPs by the bilayer membrane of the RBCs, which is directly related with the MNPs size,

103


shape and composition (4). Overall, the proposed microfluidic methodology represents a newconcept for nanomedicine, allowing for a more accurate evaluation of the haemocompatibilityof MNPs targeting clinical applications.

AcknowledgementsThis work was co-financed by FCT Ð Fundação para a Ciência e a Tecnologia and FEDERunder Programe PT2020 (Project UID/EQU/50020/2013). R.O.R. acknowledges the Ph.D.scholarship SFRH/BD/97658/2013 granted by FCT. A.M.T.S acknowledges the FCT Investi-gator 2013 Programme (IF/01501/2013), with financing from the European Social Fund andthe Human Potential Operational Programme.

References(1) Hervault, A.; Thanh, N.T.K. Nanoscale. 2014, 6, 11553.(2) Ito, A.; et al. J. Biosci. Bioeng. 2005, 100, 1.(3) Sabo, A.; et al. Int. J. Clin. Pharmacol. Ther. Toxicol. 1993, 31, 1.(4) Curtis, E.M.; Bahrami, A.H.; Weikl, T.R.; Hall, C.K. Nanoscale. 2015, 7, 14505.

104


Perplexities of Cerebral Blood Flow and Oxygen

Metabolism

Constantinos Hadjistassou, Keri Moyle, Yiannis VentikosDepartment of Engineering, Research & Technology Bld, Rm A-12a, Markou, Drakou 8, Engomi 2409,

Nicosia, Cyprus

Functional MRI (fMRI) currently enjoys widespread adoption in applications spanning frommapping brain activity to neuroleadership. Yet the interpretation of the blood oxygenation leveldependent (BOLD) fMRI signal remains challenging. Motivated by the need to decipher thephysiological and physical underpinnings behind BOLD fMRI, we present a computationalcapillary-tissue system capable of tracing venous haemoglobin saturation. Oxygen release isgoverned by the haemoglobin reaction kinetics while brain activation is mimicked by tran-sitions in cerebral blood flow (CBv) and oxidative metabolism (CMRO2). Capillary venoushaemoglobin saturation profiles and peak oxygenation results, deriving from a 50% and a 25%increase in CBv and CMRO2, respectively, yield results within physiological limits exhibit-ing very good correlation with the BOLD signal of short-duration stimuli. The last part ofthe investigation deals with neurovascular effects as they pertain to the initial dip - an earlyephemeral undershoot of the BOLD signal. Model findings demonstrate that a pre-requisite forthe manifestation of the initial dip rests on a time delay in the onset of increased CBv relativeto CMRO2.

105


Complex turbulent swirling flow analysis

Ðorđe. S. Čantrak and Novica Z. JankovićUniversity of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade 35, Republic of

Serbia

Study of the complex three-dimensional, non-homogeneous, anisotropic turbulent swirlingvelocity field in pipe generated by the axial fans is presented here. Research of the influence ofthe type and duty points of the axial fans on turbulence structure and transfer mechanism isreported. Statistical data analysis and correlation-spectral theory of turbulence is employedfor the study of the complex interactions between the average and fluctuating velocity fieldsthat characterize the processes of turbulent transfer [1-3]. Here is presented research of theaxial fan geometry impact on the skewness and flatness factors, as well on the generation ofthe vorticity field and vortex core precession movement [1,3]. Vortex core dynamics and thestatistical characteristics of the turbulent swirling flow in straight pipe behind the axial fansare calculated on the basis of the experimental data obtained by use of the stereo particleimage velocimetry (SPIV), high speed SPIV (HSS PIV) and laser Doppler anemometry (LDA)[1-5]. Anisotropy invariant maps are calculated on the basis of the measured turbulent stressesfor various fan blade angles, but for one rotation number. In this way are obtained conclusionson the influence of the fan duty point on anisotropy and turbulence structure in various flowregions.

Keywords: turbulence, swirling flow, anisotropy, invariants, LDA, PIV.

AcknowledgmentsMinistry of Education, Science and Technological Development, Republic of Serbia supportedthis work with Project No. TR 35046, what is gratefully acknowledged.

References

[1] Ð. Čantrak, Analysis of the vortex core and turbulence structure behind axial fans ina straight pipe using PIV, LDA and HWA methods, Ph.D. thesis, Univ. Belgrade, Fac. Mech.Eng., Belgrade, 2012.

[2] Ð. Čantrak, N. Janković, Investigation of the turbulent swirl flow in pipe generated by

106


axial fans using PIV and LDA methods, Theor. Appl. Mech., Vol. 42, Issue 3, (2015), 211-222.[3] Ð. S. Čantrak, N. Z. Janković, M. R. Lečić, Laser Insight into the Turbulent Swirl Flow

behind the Axial Flow Fan, Proc. ASME Turbo Expo 2014: Turbine Technical Conference andExposition, GT 2014, Technical track: Fans and Blowers, ASME TURBO EXPO 2014, June16 20, 2014, Düsseldorf, Germany, GT2014-26563, pp. V01AT10A024, 10 pages, 2014.

[4] J. Ilić, S. Ristić, Ð. Čantrak, N. Janković, M. Srećković, The Comparison of Air FlowLDA Measurement in Simple Cylindrical and Cylindrical Tube with Flat External Wall, FMETransactions 41(4) (2013), 333 341.

[5] P. Mattern, S. Sieber, Ð. Čantrak, F. Fröhlig, S. Caglar, M. Gabi, Investigations onthe swirl flow caused by an axial fan: A contribution to the revision of ISO 5801, Fan 2012,International Conference on Fan Noise, Technology and Numerical Methods, Senlis, France, 1820.04.2012, CD Proc. (2012), 11 pages, fan2012-68-MATTERN.

107


Instability of oscillatory pipe flow of wormlike micellar

solutions

J. Ortín, C. Fleming, L. Casanellas, J. Clopés, L. Ramírez de la Piscina, E. MecaUniversitat de Barcelona, Facultat de Física, Dept. ECM, C/ Martí i Franqués 1, 08028 Barcelona, (Spain)

The oscillatory flow of giant micellar solutions in a vertical pipe can be viewed as the super-position of standing viscoelastic shear waves. The parallel shear flow is increasingly reversingat increasing driving frequencies. Beyond a critical driving amplitude, strongly dependent ondriving frequency, this flow is unstable against the formation of axisymmetric vortex rings. Inthis work we present a combined experimental, numerical and theoretical effort to understandthe origin of this instability.

108


Studying and controlling drop motion on inclined surfaces

Daniele FilippiUniversitá di Padova

We report an experimental study of small water droplets sliding on flat substrates decoratedwith a periodic pattern of strips alternating hydrophobic and hydrophilic areas. Dependingon the substrate properties and control parameters, a jerkily motion featuring an evidentstick-slip dynamics is observed [1]. Similar measurements have been performed also withwater drops on chemically heterogeneous patterns formed by hydrophilic and hydrophobicdomains of different shape (stripes, squares and triangles) arranged in different patterns [2-3].The wettability contrast between the hydrophilic and hydrophobic regions causes the drop toundergo a particular stick-slip dynamics characterized by steps of the front and rear contactpoints and a mean velocity depending on the pattern geometry: chemical patterns can beexploited to passively control drop velocity. We also present preliminary results about thesliding of drops across chemical step tilted with respect to the down plane direction; theaim of this work is the study of deviation and the behavior of the dropletÕs contact line athydrophilic/hydrophobic interface [4].

[1] M. Sbragaglia, L. Biferale, G. Amati, S. Varagnolo , D. Ferraro, G. Mistura, M. Pierno,Sliding drops across alternating hydrophobic and hydrophilic stripes, Phys. Rev. E 89, 012406(2014)

[2] S. Varagnolo, D. Ferraro, P. Fantinel, M. Pierno, G. Mistura, M. Sbragaglia, G. Amati,L. Biferale. Stick-slip sliding of water drops on chemically heterogeneous surfaces, Phys. Rev.Lett . 111, 066101 (2013)

[3] S. Varagnolo, V. Schiocchet, D. Ferraro, M. Pierno, G. Mistura, M. Sbragaglia, A. Gupta,G. Amati, Tuning drop motion by chemical patterning of surfaces, Langmuir 30, 2401-2409(2014)

[4] C. Semprebon, S. Varagnolo, D. Filippi, M. Pierno, M. Brinkmann, G. Mistura, Deviationof drops at chemical steps, in preparation.

109


Role of inertia in the rheology of amorphous systems: a

finite element based elasto plastic model

Kamran Karimi and Jean-Louis BarratUniv. Grenoble Alpes and CNRS, LiPhy, F-38000 Grenoble, France

A simple Finite Element (FE) analysis with varying damping strength is used to model theathermal shear rheology of densely packed glassy systems at a continuum level. We focus on theinfluence of dissipation mechanism on bulk rheological properties. Our numerical studies, doneover a wide range of damping coefficients, identify two well-separated rheological regimes alongwith a cross-over region controlled by a critical damping. In the overdamped limit, inertial effectsare negligible and the rheological response is well described by the commonly observed Herschel-Bulkley equation. In stark contrast, inertial vibrations in the underdamped regime prompt asignificant drop in the mean-stress level, leading to a non-monotonic constitutive relation. Theobserved negative slope in the flow curve, which is a signature of mechanical instability and thuspermanent shearbanding, arises from the sole influence of inertia, in qualitative agreement withthe recent molecular dynamics study of Nicolas et al. [1].(Effects of inertia on the steady-shearrheology of disordered solids. arXiv preprint arXiv:1508.06067, 2015.)

110


Colloidal Microworms Propelling via a Cooperative

Hydrodynamic Conveyor- Belt

Fernando Martinez Pedrero, Antonio Ortiz Ambriz, Ignacio Pagonabarraga, and Pietro TiernoUniversitat de Barcelona, Departament d’Estructura i Constituents de la Matéria, Av. Diagonal 647, 08028

Barcelona (Spain)

We study propulsion arising from microscopic colloidal rotors [1,2] dynamically assembledand driven in a viscous fluid upon application of an elliptically polarized rotating magneticfield. Close to a confining plate, the motion of this self- assembled microscopic "worm" resultsfrom the cooperative flow generated by the spinning particles such as an hydrodynamic"conveyor-belt" effect. Chains of rotors propels faster than individual ones, until reaching asaturation speed at distances where flow additivity vanishes. By combining experiments withtheoretical arguments, we elucidate the underlying mechanism of motion and fully characterizethe propulsion speed in terms of the external field parameters.

References[1] P. Tierno, R. Golestanian, I. Pagonabarraga, and F. Sagués, Controlled Swimming in

Confined Fluids of Magnetically Actuated Colloidal Rotors, Phys. Rev. Lett, 101, 218304 (2008)[2] P. Tierno, S. Schreiber, W. Zimmermann, and T. M. Fischer Shape Discrimination with

Hexapole-Dipole Interactions in Magic Angle Spinning Colloidal Magnetic Resonance J. Am.Chem. Soc., 131, 5366

111


Numerical Analysis of blood flow in the common carotid

artery bifurcation and influence of non-Newtonian blood

rheological properties on blood flow

N. Antonova, D. Xu, I. Velcheva, E. Kaliviotis, P. ToshevaDepartment of Biomechanics, Institute of Mechanics to the Bulgarian Academy of Sciences, Akad. G.Bonchev

str., Bl.4, 1113 Sofia, Bulgaria

Objective: To analyze numerically the time-varying blood flow in the common carotid artery(CCA) bifurcation on the basis of Navier-Stokes equations. for four different cases, includingcases without stenosis and with one, two and three stenoses at different sites in the vicinity of thebifurcation. The study aims to review different rheological models, describing non-Newtonianblood properties and used in CFD, which will help to evaluate the role of the complex rheolog-ical behaviour of blood on blood flow in the common carotid artery (CCA) bifurcation.Materials and Methods: The cases studied were: a) without stenoses, b) with one stenosis up-stream the bifurcation, c) with two opposite stenoses upstream the bifurcation and d) with anadditional stenosis on the apex of the bifurcation. The blood flow in the arteries is modeled asincompressible viscous flow. The governing Navier-Stokes equations describing pulsatile, three-dimensional flow of an incompressible Newtonian fluid are approximated using a finite volumemethod. To create the complicated shape of the computation area a CAD system is appliedwith tetrahedral elements The mesh was generated via a geometry reconstruction and importedinto a Computational Fluid Dynamics (CFD) solver.Results: The numerical results of the blood flow in the common carotid artery (CCA) bifurca-tion give a detailed picture of the axial and radial velocity distribution and presented as velocityand vorticity magnitudes. The structures of the flow around the bifurcation from the commoncarotid artery (CCA) to the internal carotid artery (ICA) and external carotid artery (ECA)are obtained considering characteristic time points for one pulse wave period For the case ofcarotid bifurcation without stenoses results for the axial velocity distribution are presented insix characteristic time points of the pulse wave: T=0 s, 0.1s 0.2s, 0.3s, 0.4s, 0.5s. The axialvelocity distribution and wall shear stress (WSS) distribution and contours are presented. Anumber of models describing non-Newtonian rheological properties are analysed as power-lawmodel, the Herschel-Bulkley, the Casson models and others. The role of the complex blood rhe-

112


ological behaviour on blood flow in the common carotid artery (CCA) bifurcation is discussed.Discussion: The obtained velocity and WSS distribution around the bifurcation allow a pre-diction of the probably sites of stenosis growth. The recirculation zone behind the stenosis isthe area of low WSS. Thus this area is the most probable one for monocytes and platelet ag-gregation and thrombosis formation. More specifically, it was observed that the appearance ofstenotic regions upstream the bifurcation affect both the velocity and vorticity characteristics,whereas a stenosis on the apex of the bifurcation seems to have a small effect on the vortic-ity characteristics downstream the flow in the ECA and ICA. The analysis of the rheologicalmodels describing non-Newtonian rheological behavior of whole blood and the possibility touse them in CFD models, considering the complex blood flow properties is important for thedetailed picture of blood flow in CCA bifurcation.Keywords: 3D numerical calculations, CCA bifurcation, stenosis, velocity and WSS distribution,velocity and vorticity magnitude, non-Newtonian rheological models

113


Tumbling in an Extensional Flow

Emmanuel Lance Chrisopher VI M. Plan and Dario Vincenzi,Universite Nice Sophia Antipolis, Laboratoire de Mathématiques J.A. Dieudonné UMR 7351 CNRS UNS, Parc

Valrose, 06108 Nice Cedex 02, France

We study the dynamics of a semi-flexible polymer in a planar extensional flow. The polymeris modelled as a trumbbell, i.e. three beads joined by two rigid links. We show that a semi-flexiblepolymer undergoes an aperiodic tumbling motion resulting from a sequence of folding events.The probability distribution of the tumbling time is exponential with a time scale exponentiallydecreasing with the Weissenberg number.

114


Dynamics of thin fluid films with thermal fluctuations

Daniele BelardinelliDepartment of Physics and INFN, University of Rome Tor Vergata, Via Della Ricerca Scientifica 1, 00133

Rome, Italy

We consider the influence of thermal fluctuations on the dynamics of thin fluid films closeto solid boundaries. Working within the stochastic lubrication approximation, we explore themodifications induced by thermal fluctuations to the classical (i.e. zero temperature limit)profiles describing the behaviour of a liquid wedge close to solid boundaries. The problemstudied is a pre-requisite to go deeper into the non-hydrodynamical origin of the slip length,the effect which must cure the singular behaviour of the Navier-Stokes equations close to thecontact line.

115

Index

Čantrak, 106

A. Vilfan, 44

Abade, 84

Abba, 33

Ahunbay, 78

Alards, 25

Alves, 76

Ambrus, 57

Andersson, 47, 56

Angilella, 81

Antonova, 112

Aplinc, 41

Araújo, 99

Ardeshiri, 32, 88

Arietaleaniz, 98

Arnaudov, 12

Ascione, 80

Bañobre-López, 103

Baaijens, 65

Babic, 44

Babler, 55

Ballesta, 76

Barrat, 58, 110

Beale, 56

Belardinelli, 115

Bellini, 54

Benkeddad, 88

Benzi, 20, 89, 90

Biciusca, 82

Biferale, 21, 52, 61, 71

Boffetta, 22, 23, 49

Borgnino, 49

Brandt, 68, 83

Breugem, 68

Bunning, 30

Bustamante, 21, 93

Buzzicotti, 21, 71

Caballero, 83

Callegari, 102

Calzavarini, 32, 51, 88

Campo-Deaño, 35, 100

Candelier, 81

Casanellas, 108

Caserta, 80

Cebers, 45

Cencini, 49

Cerbino, 79

Chamorro, 95

Clercx, 25

116

INDEX

Clopés, 108Corbetta, 89, 90Costa, 68Covas, 48Cristea, 82Cronin, 28

D. Pinho, 100Dawson, 62De Pietro, 61De Rosis, 96De Santi, 33, 69DeLillo, 23Devailly, 62Dias, 24Dietrich, 60, 64, 77, 87Dobnikar, 44Dollet, 40Dominguez, 87Dzhonova, 50

Einarsson, 81Ekiel-Jezewska, 74Elahi, 102Erglis, 45Eskandari, 77Espinoza, 47Evans, 30, 63

Farutin, 39Feng, 12Fielding, 10Filippi, 109Fleming, 108Franosch, 92

Frisch, 71

Fuchs, 84

G.Volpe, 102

Galindo-Rosales, 35

Gallo, 103

Garaboa-Paz, 27

Garzó, 95, 97

Gekle, 42, 43

Giavazzi, 79

Gigan, 102

Gomes, 103

Gonnella, 82

Gruber, 84

Guazzelli, 9

Guckenberger, 42

Guido, 80

Gupta, 26

Höskuldsson, 94

Hadjistassou, 105

Hidalgo, 98

Hilliou, 48

Holzner, 55

Howe, 14

Hu, 39

Janković, 106

Javed, 66

Jonsdottir, 94

Kahler, 37

Kaliviotis, 112

Karimi, 110

Kinzelback, 55

INDEX 117

INDEX

Kitenbergs, 45

Kokot, 44

Kos, 85

Krueger, 72

Kruusma, 8

Kunnen, 25

Lai, 39

Lamura, 82

Lauga, 73

Lee, 89, 90

Lehnert, 56

Leveque, 96

Li, 86

Liberzon, 55

Lima, 100, 103

Lindner, 17

Lisjak, 29

Lohse, 6

Lundell, 81

Luthi, 55

M.Vilfan, 29

Mailybaev, 61

Majaron, 29

Malgaretti, 64, 87

Marin, 37

Martínez-Aranda, 35

Martinez, 62

Martinez Pedrero, 111

McHale, 66

Meca, 108

Mehlig, 81

Mertelj, 29

Miao, 28, 86Michelin, 73Misbah, 39Mohoric, 44Montenegro-Johnson, 73Moussa-Ider, 42Moyle, 105Muñuzuri, 27Muntean, 89, 90Murray, 21, 93Musacchio, 22, 23

Newton, 66Nicolas, 58Novica, 106Nunes, 99

Olla, 33, 69Ortín, 108Ortiz Ambriz, 111Osterman, 44Ouali, 66

Pérez-Muñuzuri, 27Pagonabarraga, 31, 38, 98, 111Perlekar, 52Peters, 65Peyla, 39Picano, 68, 83Pinçe, 102Pinho, 5, 100Pinkevych, 63Pires, 35Piretto, 22Plan, 114

118 INDEX

INDEX

Poon, 62

Popescu, 60, 64, 77, 87

Procaccia, 4

Puertas, 84

Puosi, 58

Rafai, 39

Rajaei, 25

Ramírez de la Piscina, 108

Ravnik, 41, 85

Ray, 71

Reshetnyak, 30, 63

Ripoll, 53

Rodrigues, 103

Roos, 86

Rossi, 37

Rottler, 58

Roversi, 54

Sabareesh, 102

Saha, 55

Sahoo, 36

Santos, 34, 97

Sardina, 83

Sbragaglia, 26

Scagliarini, 38

Schmitt, 32, 88

Schwarz-Linek, 62

Shirtcliffe, 66

Silva, 103

Slowicka, 74

Sofonea, 57, 82

Soos, 55

Souissi, 32, 88

Sozza, 23

Stocker, 11

Stone, 12

Stoyanov, 12

Subota, 63

Succi, 96

Sundén, 47, 56

Tasinkevych, 60, 64, 77

Tatulcenkovs, 45

Tavares, 103

Teixeira, 48

Telo da Gama, 99

Thiebaud, 39

Thordarson, 94

Tierno, 111

Toschi, 20, 25, 32, 52, 89, 90

Tosheva, 112

Trampert, 20

Tsibranska, 50

Tunesi, 54

Ubertini, 96

Uspal, 60, 64

Valdettaro, 33

Vega Reyes, 34, 95, 97

Velcheva, 112

Ventikos, 105

Verbeeten, 65

Vincenzi, 52, 114

Vlaev, 50

Voigtmann, 84

Volpe, 46, 102

INDEX 119

Wagner, 91Wajnryb, 74Wu, 39

Xu, 112

Zanchetta, 54

book of abstracts - campodeano.com of... · flowing matter 2016 book of abstracts 11th-15th january...

Documents