Automatic Mesh Motion with Topological Changes for Engine ...powerlab.fsb.hr/.../presentations/slides/slidesLucchiniZagreb2007Engine.pdf · Automatic Mesh Motion with Topological

Automatic Mesh Motion Automatic Mesh Motion

with Topological Changes with Topological Changes

for Engine Simulationfor Engine Simulation

T. LucchiniT. Lucchini, G. , G. DD’’ErricoErrico

Department of Department of EnergeticsEnergetics, Politecnico di Milano, Italy, Politecnico di Milano, Italy

H. H. JasakJasak

WIKKI Ltd, London, EnglandWIKKI Ltd, London, England

Z. Z. TukoviTukovićć

FSB, University of Zagreb, Croatia FSB, University of Zagreb, Croatia

SAE Paper 2007SAE Paper 2007--0101--01700170

TOPICSTOPICS

•• INTRODUCTIONINTRODUCTION

•• MESH MOTION FOR I.C. ENGINESMESH MOTION FOR I.C. ENGINES

�� Topological changesTopological changes

�� Automatic mesh motionAutomatic mesh motion

•• ENGINE MESH SETUPENGINE MESH SETUP

•• VALIDATIONVALIDATION

INTERACTING THERMOINTERACTING THERMO--FLUID DYNAMIC PROCESSESFLUID DYNAMIC PROCESSES

•• Turbulent, compressible flow;Turbulent, compressible flow;

•• Fuel spray;Fuel spray;

•• Ignition and combustion;Ignition and combustion;

•• Pollutants formation;Pollutants formation;

GEOMETRICAL CONSTRAINTSGEOMETRICAL CONSTRAINTS

•• Complex geometry; Complex geometry;

•• Moving boundaries;Moving boundaries;

NUMERICAL EFFICIENCYNUMERICAL EFFICIENCY

CFD SIMULATION OF I.C. ENGINESCFD SIMULATION OF I.C. ENGINES

•• COMPLEX GEOMETRY COMPLEX GEOMETRY

•• Unstructured grids;Unstructured grids;

•• Moving piston and valves, ports;Moving piston and valves, ports;

•• High mesh quality required for the whole simulation;High mesh quality required for the whole simulation;

•• MESH MOTION REQUIREDMESH MOTION REQUIRED

•• PrePre--processing mesh tools for mesh motion;processing mesh tools for mesh motion;

•• Significant manual work required;Significant manual work required;

•• Mesh motion is not solutionMesh motion is not solution--dependent;dependent;

STATE OF ART OF MESH MOTIONSTATE OF ART OF MESH MOTION

COMPLEX GEOMETRYCOMPLEX GEOMETRY

MESH MOTION REQUIREDMESH MOTION REQUIRED

AIM OF THE WORKAIM OF THE WORK

•• No preNo pre--processing. Mesh motion integrated in the processing. Mesh motion integrated in the solver, at any time step:solver, at any time step:

�� Grid points moved;Grid points moved;

�� Mesh topology eventually changed;Mesh topology eventually changed;

•• MultipleMultiple--region decomposition: in each region, mesh region decomposition: in each region, mesh motion is accommodated in different ways;motion is accommodated in different ways;

•• Combined use of different topological changes;Combined use of different topological changes;

•• Polyhedral vertex based motion solver for mesh Polyhedral vertex based motion solver for mesh deformation based on Finite Element Method (FEM);deformation based on Finite Element Method (FEM);

DEVELOPING A NEW APPROACH FOR MESH MOTIONDEVELOPING A NEW APPROACH FOR MESH MOTION

OpenFOAMOpenFOAM (Field Operation and Manipulation)(Field Operation and Manipulation)

•• C++ objectC++ object--oriented;oriented;

•• New models easily developed and tested in isolation;New models easily developed and tested in isolation;

••

OVERVIEW OF THE CODEOVERVIEW OF THE CODE

( ) ( ) 0tftf T tf

YY Y

t

ρρ µ

∂+ ∇ ⋅ + ∇ ⋅ ∇ =

∂U

solve

(

fvm::ddt(rho, Ytf)

+ fvm::div(phi, Ytf)

+ fvm::laplacian(mut, Ytf)

);

OpenFOAMOpenFOAM (Field Operation and Manipulation)(Field Operation and Manipulation)

•• Polyhedral mesh support;Polyhedral mesh support;

•• Numerical schemes available for temporal and spatial Numerical schemes available for temporal and spatial discretizationdiscretization;;

•• Reliable and validated libraries for:Reliable and validated libraries for:

�� Combustion (premixed and nonCombustion (premixed and non--premixed);premixed);

�� Complex chemistry;Complex chemistry;

�� LagrangianLagrangian spray modelling;spray modelling;

�� Turbulence (RANS and LES);Turbulence (RANS and LES);

FINITE VOLUME METHODFINITE VOLUME METHOD

MESH MOTION FOR I.C. ENGINESMESH MOTION FOR I.C. ENGINES

•• TOPOLOGICAL CHANGESTOPOLOGICAL CHANGES

�� Dynamic mesh layeringDynamic mesh layering

�� Sliding interfaceSliding interface

�� Attach/detach boundaryAttach/detach boundary

•• AUTOMATIC MESH MOTIONAUTOMATIC MESH MOTION

�� Polyhedral vertex based motion solverPolyhedral vertex based motion solver







•• Keep an optimum mesh size during the whole cycle;Keep an optimum mesh size during the whole cycle;

•• User definition: User definition: maximummaximum and and minimumminimum thicknesses, thicknesses, base surfacebase surface;;

DYNAMIC MESH LAYERINGDYNAMIC MESH LAYERING

Addition/removal of cell layers in a moving coneAddition/removal of cell layers in a moving cone














SLIDING INTERFACESLIDING INTERFACE

•• Dynamically connecting different mesh regions by point Dynamically connecting different mesh regions by point projection algorithm; projection algorithm;

•• Mesh quality is kept high, no distortions;Mesh quality is kept high, no distortions;

•• User definition of User definition of ““mastermaster”” and and ““slaveslave”” patches;patches;

Mixer vesselMixer vessel Flow control deviceFlow control device














ATTACHATTACH--DETACH BOUNDARYDETACH BOUNDARY

•• Splits the mesh in two separate regions from a list of Splits the mesh in two separate regions from a list of internal faces; internal faces;

•• Simulates valve closure;Simulates valve closure;

•• ““Minimum liftMinimum lift”” to impose valve closure;to impose valve closure;

•• No geometry modifications or No geometry modifications or ““inert cellsinert cells”” required;required;

Valve Valve

closure closure

timetime














POLYHEDRAL VERTEXPOLYHEDRAL VERTEX--BASED MOTION SOLVERBASED MOTION SOLVER

•• Grid is deformed and mesh refined around TDC;Grid is deformed and mesh refined around TDC;

•• Solve the Solve the LaplaceLaplace equation of motion;equation of motion;

•• Tetrahedral decomposition of the polyhedral mesh to Tetrahedral decomposition of the polyhedral mesh to keep the mesh valid;keep the mesh valid;

FEM decomposition of a polyhedral cellFEM decomposition of a polyhedral cell

Mesh deformation around TDC for a pentMesh deformation around TDC for a pent--roof, SI engine roof, SI engine

during the intake stroke (lift from 1 mm to 5 mm)during the intake stroke (lift from 1 mm to 5 mm)

POLYHEDRAL VERTEXPOLYHEDRAL VERTEX--BASED MOTION SOLVERBASED MOTION SOLVER

1) MOTION EQUATION1) MOTION EQUATION

( ) 0γ∇ ∇ =ui

2) NEW POINT POSITION2) NEW POINT POSITION

new old t= + ∆x x u

ENGINE MESH SETUP:ENGINE MESH SETUP:TWOTWO--STROKE ENGINESSTROKE ENGINES

TWOTWO--STROKE ENGINES: MESH SETUPSTROKE ENGINES: MESH SETUP

CylinderCylinder

Intake portsIntake ports

Exhaust portExhaust port

THREE REGIONSTHREE REGIONS

TWOTWO--STROKE ENGINES: MESH MOTIONSTROKE ENGINES: MESH MOTION

1) PISTON MOTION1) PISTON MOTION

•• dynamic layeringdynamic layering

•• deformationdeformation

2) PORTS2) PORTS--CYLINDER CONNECTIONCYLINDER CONNECTION

•• slidingsliding--interfaceinterface

COMBINED USE OF MULTIPLE COMBINED USE OF MULTIPLE

TOPOLOGICAL CHANGESTOPOLOGICAL CHANGES

ENGINE MESH SETUP:ENGINE MESH SETUP:FOURFOUR--STROKE ENGINESSTROKE ENGINES

FOURFOUR--STROKE ENGINES: MESH SETUPSTROKE ENGINES: MESH SETUP

FIVE REGIONSFIVE REGIONS

Intake and Intake and

exhaust portsexhaust ports

Remainder of Remainder of

the cylinderthe cylinder

Valve curtainsValve curtains

FOURFOUR--STROKE ENGINES: MESH MOTIONSTROKE ENGINES: MESH MOTION

1) PISTON MOTION1) PISTON MOTION



2) VALVE MOTION2) VALVE MOTION



3) VALVE CLOSURE3) VALVE CLOSURE

•• attachattach--detach boundarydetach boundary

4) CYLINDER4) CYLINDER--VALVE CURTAINSVALVE CURTAINS

•• slidingsliding--interfaceinterface

COMBINED USE OF MULTIPLE COMBINED USE OF MULTIPLE

TOPOLOGICAL CHANGESTOPOLOGICAL CHANGES

VALIDATIONVALIDATION

•• SCAVENGING IN A TWOSCAVENGING IN A TWO--STROKE ENGINESTROKE ENGINE

•• COMBUSTION IN A SIDECOMBUSTION IN A SIDE--VALVE ENGINEVALVE ENGINE

•• DIESEL ENGINE COMBUSTIONDIESEL ENGINE COMBUSTION

•• INTAKE STROKE IN A FOURINTAKE STROKE IN A FOUR--STROKE ENGINESTROKE ENGINE





SCAVENGING IN A TWOSCAVENGING IN A TWO--STROKE ENGINESTROKE ENGINE

ENGINE GEOMETRYENGINE GEOMETRY

1.05 barBoost pressure

2500 rpmSpeed

10.8Comp. Ratio

57 mmStroke

66.5 mmBore

COMPUTATIONAL MESHCOMPUTATIONAL MESH

Axial-symmetric

8000No. of cells at TDC

25000No. of cells at BDC

PHYSICAL MODELS AND PHYSICAL MODELS AND

BOUNDARY CONDITIONSBOUNDARY CONDITIONS

•• kk--εε turbulence model;turbulence model;

•• No slip at walls;No slip at walls;•• Total pressure at intake;Total pressure at intake;•• Fixed temperature at walls;Fixed temperature at walls;


EVOLUTION OF EGR AND INEVOLUTION OF EGR AND IN--CYLINDER FLOW FIELDCYLINDER FLOW FIELD


Radial velocity at different locationsRadial velocity at different locations

•• High velocities close to the scavenging portsHigh velocities close to the scavenging ports•• Tumble created by the piston motionTumble created by the piston motion


Radial velocity at different locationsRadial velocity at different locationsTurbulence intensity at different locationsTurbulence intensity at different locations

•• High uHigh u’’ produced by the incoming air jetproduced by the incoming air jet•• Turbulence decay at the end of compressionTurbulence decay at the end of compression










COMBUSTION IN A SIDECOMBUSTION IN A SIDE--VALVE ENGINEVALVE ENGINE


MV-CAGIVA GABBIANO NV 2

1000 rpmSpeed

8Comp. Ratio

73.2 mmStroke

98 mmBore


Compression-Combustion






•• Weller bWeller b--ΞΞ combustion model;combustion model;•• Fixed temperature and noFixed temperature and no--slip slip at walls;at walls;

•• Sliding interfaceSliding interface models the partial models the partial side head covering by the pistonside head covering by the piston

Predicted cylinder Predicted cylinder

pressure tracepressure trace

COMBUSTION IN A SIDECOMBUSTION IN A SIDE--VALVE ENGINEVALVE ENGINE

EVOLUTION OF THE REGRESS VARIABLE EVOLUTION OF THE REGRESS VARIABLE bb

(b=0: fully burnt, b=1: fully (b=0: fully burnt, b=1: fully unburntunburnt))

DURING THE COMBUSTION PROCESSDURING THE COMBUSTION PROCESS

•• QuasiQuasi constantconstant--volume combustion correctly predicted by the model;volume combustion correctly predicted by the model;










DIESEL ENGINE COMBUSTIONDIESEL ENGINE COMBUSTION


2.5Swirl Ratio

3100 rpmSpeed

4 barBoost pressure

SEATEK 850 PLUS

14Comp. Ratio

134 mmStroke

127 mmBore


Compression-Combustion





•• LagrangianLagrangian spray modelling;spray modelling;•• Complex chemistry and ISAT to Complex chemistry and ISAT to model combustion;model combustion;

•• RNG RNG kk--εε turbulence model;turbulence model;

DIESEL ENGINE COMBUSTIONDIESEL ENGINE COMBUSTION

•• Agreement with experimental cylinder pressure data, Agreement with experimental cylinder pressure data, LagrangianLagrangianparticles correctly tracked also with particles correctly tracked also with dynamicdynamic--layeringlayering; ;

Predicted cylinder pressurePredicted cylinder pressureFUEL INJECTION AND COMBUSTIONFUEL INJECTION AND COMBUSTION











3000 rpmSpeed

14Comp. Ratio

92 mmStroke

100 mmBore







•• Fixed temperature and noFixed temperature and no--slip slip at walls;at walls;

INTAKE STROKE IN A FOURINTAKE STROKE IN A FOUR--STROKE ENGINESTROKE ENGINE


PREDICTED FLOWPREDICTED FLOW--FIELD AND TURBULENCE INTENSITY FIELD AND TURBULENCE INTENSITY –– INTAKE STROKEINTAKE STROKE

•• Large ring vortex below the valve moving downwardLarge ring vortex below the valve moving downward


PREDICTED FLOWPREDICTED FLOW--FIELD AND TURBULENCE INTENSITY FIELD AND TURBULENCE INTENSITY –– INTAKE STROKEINTAKE STROKE

•• Turbulence generated by high velocity and flow deflectionTurbulence generated by high velocity and flow deflection


Velocity and turbulence intensity distribution across the valve Velocity and turbulence intensity distribution across the valve liftlift

Typical values of Typical values of

U/sU/spp ≈≈ 1010

correctly correctly predictedpredicted


InIn--cylinder turbulence intensity evolutioncylinder turbulence intensity evolution

' 0.5TDC pu s≅

CONCLUSIONSCONCLUSIONS


•• Engine geometries;Engine geometries;

•• Compressible flow equations;Compressible flow equations;

•• Turbulence;Turbulence;

•• Scalar transport (EGR);Scalar transport (EGR);

•• Premixed combustion;Premixed combustion;

•• LagrangianLagrangian particle tracking;particle tracking;

•• Complex chemistry;Complex chemistry;

PROPOSED MESH MOTION APPROACH SUCCESSFULLY TESTEDPROPOSED MESH MOTION APPROACH SUCCESSFULLY TESTED


•• Finite Volume Method + Moving Meshes;Finite Volume Method + Moving Meshes;

GENERALITY OF THE APPROACHGENERALITY OF THE APPROACH

•• Engines with canted valves;Engines with canted valves;

•• Rotary machines:Rotary machines:

�� WankelWankel engines;engines;

�� Automotive CFD (superchargers, fuel pumps,...);Automotive CFD (superchargers, fuel pumps,...);

DEVELOPMENTSDEVELOPMENTS

ACKNOWLEDGMENTSACKNOWLEDGMENTS

•• Dr. Dr. HrvojeHrvoje JasakJasak

•• Dr. Dr. ZeljkoZeljko TukovicTukovic

•• Dr. Dr. GianlucaGianluca DD’’ErricoErrico

•• Mr. Mario Mr. Mario MazuranMazuran and Mr. and Mr. LucianoLuciano SpaggiariSpaggiari

•• MV MV AgustaAgusta S.p.AS.p.A. and SEATEK . and SEATEK S.p.AS.p.A..

THANKS FOR YOUR ATTENTION!THANKS FOR YOUR ATTENTION!

Tommaso LucchiniTommaso Lucchini

Politecnico di Milano,Politecnico di Milano,

DipartimentoDipartimento di di EnergeticaEnergetica

Via La Via La MasaMasa, 34, 34

20158 Milano (Italy)20158 Milano (Italy)

+39 02 23 99 86 36+39 02 23 99 86 36

[email protected]@polimi.it

www.engines.polimi.itwww.engines.polimi.it

Documents

Automatic Mesh Motion with Topological Changes for Engine ...powerlab.fsb.hr/.../presentations/slides/slidesLucchiniZagreb2007Engine.pdf · Automatic Mesh Motion with Topological