Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Sh h k S K H i Pit hShashank, Seongwon Kang, Heinz Pitsch

Department of Mechanical engineering Stanford UniversityDepartment of Mechanical engineering, Stanford University, Center for Turbulence Research, Stanford University

Supported by GCEP, Stanford and Joel H. Ferziger memorial fellowship

Motivation

• Automotive industry major contributor to green house gas emission

R d fReduce usage of cars(Use bikes!)Efficient enginesgLow emission engines

• Paradigm shift in IC engine design• Paradigm shift in IC engine designExperiments expensiveRole of simulation critical

• For simulation to be effectiveNeed for predictive capabilityNeed for predictive capabilityLarge Eddy Simulation (LES)

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Introduction

Issues in LES modeling IC engines

• Complex geometryMoving parts

• Complex turbulent flowWide range of length scalesg gGlobal coherent structuresBroad time scales

• Multi-physics interactionCombustionMultiphase flowTurbulence

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ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Strategy

LES approach• Structured staggered meshesS uc u ed s gge ed es es• ALE technique for simple geometry changes

(piston) • Immersed boundary approach for• Immersed boundary approach for

• Representation of complex geometry • Describe complex geometry changes (valves)

Advantages• Computationally inexpensive

• Structured meshesStructured meshes• Staggered mesh requires less stencil points

for same accuracyE i i l h• Energy conserving numerical schemes

• Higher order numerical schemes• Fast mesh generation

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

g

Computational tool

Scheme properties*• Arbitrary accuracy for all terms

Vortex convection

• Primary conservation (mass & momentum)• Secondary conservation (kinetic energy)

i h• Even withNon uniform meshes Cylindrical coordinates

Viscous decay

Cylindrical coordinatesVariable density

New high order boundary conditions• Primary conservation• Good secondary conservation

C li d i l di

Energy conservationν=0, D=0

Cylindrical coordinates• Full handling of arbitrary high order of

accuracy

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

y* Desjardins et. al , vol. 227, JCP 2008

Immersed Boundary Method

Equations of motion in IB fluidΩ

Γ

solidΩ

ΓIB

fluidΩ

Reconstruction IB - Direct forcing • Replace momentum equation by

solidΩp q y

interpolation near IB surface• Decouple fluid and solid regions

M ti f fl id i

ΓIB

fl idΩ• Mass conservation for fluid regionsBest suited to finite difference

fluidΩ

solidΩ

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

ΓIB

Approximate Domain Method

• Find intersection points between surface and mesh τa

Tag cells lacking fluid points in the original stencil

• Reconstruct these points from

a

• Reconstruct these points from neighboring fluid points

Boundary condition for fluid cells τIB

computationNo change in mass conservation fluid side Conserve mass on IB surface

Least squares minimization

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

* S. Kang et. al , vol. 228, JCP 2009

Approximate Domain Method

• AdvantagesDecouple fluid solution domain from solidCan treat one cell thick interface Q i l l tiQuasi-local mass conservation

• DisadvantagesOnly quasi-local mass conservation

τa

y qNo kinetic energy conservation across IB surface

i h h l i iτIBHigh mesh resolution requirements

Linear interpolationNon conservation of Kinetic

IB

Non conservation of Kinetic energy

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Flow bench experiments

Flow bench setup • Steady configuration

Port diameter

Steady configuration• Used to test valve shapes

Maximize discharge coefficient Head diameter

Lift

• Challenging simulationHighly turbulent recirculating flowWid f l th lWide range of length scalesWell suited for LES

Low lift

Medium lift High lift

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Axi-symmetric Valve

34.2 mm

Axi-symmetric flow bench • Reynolds number 30000y• 3 million mesh points• Fully developed pipe inflow 40.2 mm

10 mm

• Dynamic Lagrangian SGS model

• 3 flow through time in 24 hours3 flow through time in 24 hours over 32 processors

• LDA measurements*120120 mm

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

* L. Thobois et. al , SP-1888, SAE 2004

Axi-symmetric Valve

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Axi-symmetric Valve

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

PSA Flow bench

PSA flow bench • Valve lift L = 8 mm• Reynolds number 150 000Reynolds number 150,000• 9 million mesh points• 1 flow through time

took 24 hours on 80 processors • Mean flow DGV

*measurements*

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

* L. Thobois et. al , SP-1888, SAE 2004

PSA Flow bench

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

GM Flow bench

GM flow bench • Valve lift L = 15mm• Maximum mean velocity 64 m/s• Reynolds number 300,000• 8 million mesh points• 8 million mesh points

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Summary

• Structured grid framework with Immersed Boundary method valid g yalternative to simulate flow around complex geometries

• Reconstruction Immersed Boundary method a powerful technique with some specific advantageswith some specific advantages

• Kinetic energy and local mass conservation issues needs to be looked into

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Thank You

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes

Computational tool

ShashankStanford University Application of Immersed Boundary technique for Large Eddy Simulation of IC engine processes