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