Drag Reduction in Turbulent Flows over Super-hydrophobic Micro/nano

Structured Biomimetic Surfaces Usman Bin Shahid, PI: Anne-Marie Kietzig

Department of Chemical Engineering

McGill University, Montreal, Canada

Superhydrophobicity is attributed to both

surface structure and surface chemistry. Surface

structuring increases the possible hydrophobicity

of a surface beyond what is attainable due to

surface chemistry alone. Investigations on the

influence of surface structure and hydrophobicity

on hydrodynamic drag indicate significant slip

enhancements and hence hydrodynamic drag

reductions.

The Experimental Setup Calculations

Calculations for Flow Rates

Dimensions /mm

Kinematic

Viscosity of

H2O (m2/s)

DH

/mm

Velocity

range

Laminar

Flow (mm/s)

Flow Rates

(mL/min)

Width Height Min Max Min Max

38.1 7.9

1.004E-06

13.1 0.77 153.4 13.8 2771

2.5 0.7 1.1 9.18 1835.9 0.96 192.7

12.0 1.2 2.2 4.60 920.3 3.98 795.1

5.0 1.4 2.2 4.59 917.9 1.93 385.5

(Left to right) Micro-channel, Peristaltic

Pump, Pressure transducers

*∆𝑃 = 𝜌𝑉2𝒇𝐿

2𝐷𝐻

Acknowledgement

∆𝑃 – Pressure drop

𝜌 – Fluid density

V – Velocity of the flow

f – Friction factor

L – Length of channel

DH – Hydraulic diameter

Understanding the influence of the surface on the

drag-reduction by measuring the inlet/outlet pressure

difference

*Blevins R D 1984 Applied Fluid Dynamics Handbook (New

York: Van Nostrand-Reinhold)

Authors would like to thank McGill University

for funding this project through the SURE

Programme.

I would like to also thank Mohammad

Bajmmal (grad student) for his contribution in

helping set up the transducers and its circuit.

Also Anjishnu Sarkar and Jorge Lehr

(grad students) for their time and suggestions

for the micro-channel design. 5 mm

1.4 mm

23 cm

Introduction

Objective

The objective is to design a setup to be able

to measure pressure drop across such surfaces

and consequently characterize them with regard

to their potential in reducing drag. Surfaces with

enhanced drag reduction are inspired by the

Biomimicry of shark skin

Design Workplan

Future Prospects

Factors considered while designing the channel:

• Set Bench Mark with Other Researches

Similar DH (hydraulic diameter) sought

Lengths manipulated to give same DH

• Surfaces Geometrics Limitations

Stages allow a 5 x 5 mm x-y range

Time constraint to make surfaces

• Entrance Length for Fully Developed Laminar/Turbulent Flows

Empirical equations allowed for an estimate

60mm of developing length factored in design

• Pump Selection

Very small flow rates (range of 1 – 12mL/min)

Accuracy of ±2 mL/min

Controllable flow rates

• Pressure Transducers

Range 0-10 kPa

Accuracy 0.25% (FS)

Circuit for Signal Amplification

Signal Calibration and conversion through LabView

This channel has been designed to measure the inlet/outlet pressure difference. Further

calibration will be carried on in a future project. The design‘s flexibility and transparent nature

allows for flow visualization by tracer experiments, and measurements over different surfaces

like hydrophobic and hydrophilic.

A) 3d Model for Channel. B) Amplification Circuit