engineFoam tutorial with different flame-wrinkling (Xi) modelhani/kurser/OS_CFD_2018/SandipWadekar/sli… · Sandip Wadekar Mechanics and Maritime Sciences, Chalmers University of

engineFoam tutorial

engineFoam tutorial with different flame-wrinkling (Xi)model

Sandip Wadekar

Mechanics and Maritime Sciences,Chalmers University of Technology,

Gothenburg, Sweden

2018-11-29

Sandip Wadekar CFD with OpenSource Software, 2018 2018-11-29 1 / 38

engineFoam tutorial

Subsection

A Brief tutorial for engineFoam in OpenFOAM

A brief introduction of premixed turbulent combustion.

engineFoam solver:

engineFoam.C filesrc/engine/engineTime/engineTime.C filebEqn.H filebEqn.H : new flame wrinkling models

Setup a case:

thermophysical and combustion propertiesInitial and boundary conditionsrun the case

Results


engineFoam tutorial

Subsection

Premixed combustion

Fuel and oxidizer are mixed prior to the ignition.

Reaction occurs at the surface of the flame.

Flame front propagates from burnt mixture to un-burnt mixture.

Flame propagation can be defined by the progress variable c

c =T − TuTb − Tu

(1)

For the burnt gas c = 1, and for un-burnt gases c = 0.

But in engineFoam solver, the flame front propagation is modeled byregression variable b, with the relation b = c− 1.

Flame propagation is modeled by solving transport equation ofregression variable.


engineFoam tutorial

Subsection

engineFoam solver

The engineFoam solver involves:

Compressible

Transient

Heat transfer

Chemistry

Turbulence

Combustion

Premixed fuel-oxidizer

Partially-premixed fuel-oxidizer

moving mesh

time defined in crank-angle degree (CAD)


engineFoam tutorial

Subsection

closure problem

Fluid flow:

Conservation of mass

Conservation of momentum

Conservation of energy

Equation of state

Combustion:

progress/regress variable

species/mass-fraction equation


engineFoam tutorial

Subsection

create new engineFoam solver

Copy and rename the solver

cd $WM_PROJECT_USER_DIR

cp -r $FOAM_APP/solvers/combustion/engineFoam myengineFoam

cd myengineFoam

Now, we also need to modify the files in Make directory,

sed -i s/"engineFoam"/"myengineFoam"/g Make/files

sed -i s/"FOAM_APPBIN"/"FOAM_USER_APPBIN"/g Make/files

Check: engineFoam.C

EXE = $(FOAM_USER_APPBIN)/myengineFoam

Then compile the solver: wmake


engineFoam tutorial

Subsection

engineFoam.C#include "fvCFD.H"

#include "engineTime.H"

#include "engineMesh.H"

#include "psiuReactionThermo.H"

#include "turbulenceModel.H"

#include "laminarFlameSpeed.H"

#include "ignition.H"

#include "Switch.H"

#include "OFstream.H"

#include "mathematicalConstants.H"

#include "pimpleControl.H"

#include "fvIOoptionList.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

int main(int argc, char *argv[])

{

#include "setRootCase.H"

#include "createEngineTime.H"

#include "createEngineMesh.H"

#include "readCombustionProperties.H"

#include "createFields.H"

#include "createFvOptions.H"

#include "initContinuityErrs.H"

#include "readEngineTimeControls.H"

#include "compressibleCourantNo.H"

#include "setInitialDeltaT.H"

#include "startSummary.H"

pimpleControl pimple(mesh);

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


engineFoam tutorial

Subsection

engineFoam.C

Info<< "\nStarting time loop\n" << endl;

while (runTime.run())

{

#include "readEngineTimeControls.H"

#include "compressibleCourantNo.H"

#include "setDeltaT.H"

runTime++;

Info<< "Crank angle = " << runTime.theta() << " CA-deg" << endl;

Info<< "This is myengineFoam " << endl;

mesh.move();

#include "rhoEqn.H"

// --- Pressure-velocity PIMPLE corrector loop

while (pimple.loop())

{

#include "UEqn.H"

#include "ftEqn.H"

#include "bEqn.H"

#include "EauEqn.H"

#include "EaEqn.H"

...

...

}


engineFoam tutorial

Subsection

src/engine/engineTime/engineTime.C file

// * * * * * * * * * * * * * Private Member Functions * * * * * * * * * * * //

void Foam::engineTime::timeAdjustment()

{

deltaT_ = degToTime(deltaT_);

endTime_ = degToTime(endTime_);

if

(

writeControl_ == wcRunTime

|| writeControl_ == wcAdjustableRunTime

)

{

writeInterval_ = degToTime(writeInterval_);

}

}

// * * * * * * * * * * * * * * * * Constructors * * * * * * * * * * * * * * //

//- Construct from objectRegistry arguments

Foam::engineTime::engineTime

(

const word& name,

const fileName& rootPath,

const fileName& caseName,

const fileName& systemName,

const fileName& constantName,

const fileName& dictName

)

:


engineFoam tutorial

Subsection

src/engine/engineTime/engineTime.C fileTime

(

name,

rootPath,

caseName,

systemName,

constantName

),

dict_

(

IOobject

(

"engineGeometry",

constant(),

*this,

IOobject::MUST_READ_IF_MODIFIED,

IOobject::NO_WRITE,

false

)

),

rpm_(dict_.lookup("rpm")),

conRodLength_(dimensionedScalar("conRodLength", dimLength, 0)),

bore_(dimensionedScalar("bore", dimLength, 0)),

stroke_(dimensionedScalar("stroke", dimLength, 0)),

clearance_(dimensionedScalar("clearance", dimLength, 0))

{

// geometric parameters are not strictly required for Time

dict_.readIfPresent("conRodLength", conRodLength_);

dict_.readIfPresent("bore", bore_);

dict_.readIfPresent("stroke", stroke_);


engineFoam tutorial

Subsection


dict_.readIfPresent("clearance", clearance_);

timeAdjustment();

startTime_ = degToTime(startTime_);

value() = degToTime(value());

deltaTSave_ = deltaT_;

deltaT0_ = deltaT_;

// * * * * * * * * * * * * * * * Member Functions * * * * * * * * * * * * * //

Foam::scalar Foam::engineTime::degToTime(const scalar theta) const

{

// 6 * rpm => deg/s

return theta/(6.0*rpm_.value());

}

Foam::scalar Foam::engineTime::timeToDeg(const scalar t) const

{

// 6 * rpm => deg/s

return t*(6.0*rpm_.value());

}

Foam::scalar Foam::engineTime::pistonPosition(const scalar theta) const

{

return

(

conRodLength_.value()

+ stroke_.value()/2.0

+ clearance_.value()

)


engineFoam tutorial

Subsection


- (

stroke_.value()*::cos(degToRad(theta))/2.0

+ ::sqrt

(

sqr(conRodLength_.value())

- sqr(stroke_.value()*::sin(degToRad(theta))/2.0)

)

);

}

Foam::dimensionedScalar Foam::engineTime::pistonDisplacement() const

{

return dimensionedScalar

(

"pistonDisplacement",

dimLength,

pistonPosition(theta() - deltaTheta()) - pistonPosition().value()

);

}

Foam::dimensionedScalar Foam::engineTime::pistonSpeed() const

{

return dimensionedScalar

(

"pistonSpeed",

dimVelocity,

pistonDisplacement().value()/(deltaTValue() + VSMALL)

);

}


engineFoam tutorial

Subsection

bEqn.H file

This file contains:

Transport equation of regression variable

Reaction source term

Models for laminar flame speed

unstrainedequilibriumtransport

Models for flame wrinkling:

fixedalgebraic (or weller model)transport


engineFoam tutorial

Subsection

bEqn.H: Implementation

Transport equation of regression variable:

∂

∂t(ρb) +∇.(ρub)−∇.( µt

Sct∇b) = −ρuSuΞ|∇b| (2)

This equation is implemented as follow:

fvScalarMatrix bEqn

(

fvm::ddt(rho, b)

+ mvConvection->fvmDiv(phi, b)

+ fvm::div(phiSt, b, "div(phiSt,b)")

- fvm::Sp(fvc::div(phiSt), b)

- fvm::laplacian(turbulence->alphaEff(), b)

==

fvOptions(rho, b)

);


engineFoam tutorial

Subsection

bEqn.H: Laminar flame speed

The laminar flame speed can be calculated based on three differentmodels:

unstrained

equilibrium

transport

Implementation of the these models you can be found in to the line111-161 of bEqn.H


engineFoam tutorial

Subsection

bEqn.H: Flame wrinkling factor

The flame wrinkling factor can be calculated based on three differentmodels:

fixed: Do nothing Xi is fixed

algebraic (weller model)

Ξ∗eq = 1 + 0.62

√u′

SuRη, (3)

Ξ = 1 + 2(1− b)(Ξ∗eq − 1) (4)

Xi == scalar(1) +

(scalar(1) + (2*XiShapeCoef)*(scalar(0.5)-b))

*XiCoef*sqrt(up/(Su + SuMin))*Reta;


engineFoam tutorial

Subsection

bEqn.H: Flame wrinkling factor

transport : Xi transport equation is solvedfvScalarMatrix XiEqn

(

fvm::ddt(rho, Xi)

+ fvm::div(phi + phiXi, Xi, "div(phiXi,Xi)")

- fvm::Sp(fvc::div(phiXi), Xi)

==

rho*R

- fvm::Sp(rho*(R - G), Xi)

- fvm::Sp

( rho*max

(

sigmat - sigmas,

dimensionedScalar(sigmat.dimensions(), Zero)

),

Xi

)

+ fvOptions(rho, Xi)

);

XiEqn.relax();

fvOptions.constrain(XiEqn);

XiEqn.solve();

fvOptions.correct(Xi);

// Correct boundedness of Xi

// ~~~~~~~~~~~~~~~~~~~~~~~~~

Xi.max(1.0);

Info<< "max(Xi) = " << max(Xi).value() << endl;

Info<< "max(XiEq) = " << max(XiEq).value() << endl;

}


engineFoam tutorial

Subsection

bEqn.H: New flame wrinkling models

muppala

Ξ = 1 +0.46

LeRe∆

0.25 (u′∆SL

)0.3 (p

p0)0.2 (5)

else if (XiModel == "muppala")

{

volScalarField delta = pow(cellVolu,1.0/3.0);

volScalarField up(uPrimeCoef*sqrt((2.0/3.0)*turbulence->k()));

volScalarField Ret((rho * up* delta)/(turbulence->mu()));

dimensionedScalar pref

(dimensionedScalar("pref", p.dimensions(), 100000));

Xi == scalar(1) +

((0.46/1.0) * pow(Ret,0.25)*pow(up/Su,0.3)*pow(p/pref,0.2));

Info << "Xi-Muppala" << max(Xi).value() << endl;

}


engineFoam tutorial

Subsection

bEqn.H: New flame wrinkling models

zimont

Ξ = 1 + 0.51 (u′∆SL

)3/4 (∆

δL)1/4 (6)

else if (XiModel == "zimont")

{

volScalarField delta = pow(cellVolu,1.0/3.0);

volScalarField up(uPrimeCoef*sqrt((2.0/3.0)*turbulence->k()));

volScalarField Ret((rho * up* delta)/(turbulence->mu()));

dimensionedScalar pref

(dimensionedScalar("pref", p.dimensions(), 100000));

volScalarField dl= ( thermo.muu() / (0.7 * rhou) ) / Su0;

Xi == scalar(1) + (0.51 * pow(Ret,0.75) * pow(delta/dl,0.25));

Info << "Xi-Zimont" << max(Xi).value() << endl;

}


engineFoam tutorial

Subsection

createFields.H

need to add the cellvolu before compiling

volScalarField cellVolu // Included

(

IOobject

(

"cellVolu",

runTime.timeName(),

mesh,

IOobject::NO_READ,

IOobject::AUTO_WRITE

),

mesh,

dimensionedScalar("zero", dimVolume, 0.0)

);

compile the solver

cd $WM_PROJECT_USER_DIR/myengineFoam

wmake


engineFoam tutorial

Subsection

Case set-up

Case description

Constant

Initial and boundary conditions

system


engineFoam tutorial

Subsection

Case set-up: description

KivaTest engine geometry is used (valve is not present).premixed mixture of air-propane is used as a working fluid.Case covers only compression (-180 to 0 cad), ignition (-15 cad) andexpansion phase (0 to 60 cad).

Figure: The geometry of the kivaTest tutorialSandip Wadekar CFD with OpenSource Software, 2018 2018-11-29 22 / 38

engineFoam tutorial

Subsection

Case set-up: constant

engineGeometry :

engineMesh layered;

conRodLength conRodLength [ 0 1 0 0 0 0 0 ] 0.147;

bore bore [ 0 1 0 0 0 0 0 ] 0.092;

stroke stroke [ 0 1 0 0 0 0 0 ] 0.08423;

clearance clearance [ 0 1 0 0 0 0 0 ] 0.00115;

rpm rpm [ 0 0 -1 0 0 0 0 ] 1500;


engineFoam tutorial

Subsection


turbulenceProperties : 1. RASModel 2. LESModelsimulationType RASModel;

RASProperties :

RASModel LaunderSharmaKE;

turbulence on;

printCoeffs on;

g :

dimensions [0 1 -2 0 0 0 0];

value (0 0 0);


engineFoam tutorial

Subsection


Model DescriptionLRR Launder-Reece-Rodi RSTMLaunderGibsonRSTM Launder-Gibson RSTMLaunderSharmaKE Launder-Sharma low-Re k − ε modelRNGkEpsilon RNG k − ε modelSpalartAllmaras Spalart-Allmaras 1-eqn mixing-length modelkEpsilon Standard k − ε modelkOmegaSST k − ω − SSt modellaminar Dummy turbulence model for laminar flowrealizableKE Realizable k − ε modelv2f v2 − f model

Table: RANS turbulence model for compressible flow


engineFoam tutorial

Subsection

Case set-up: constant/thermophysicalProperties

keyword : thermoType

Possible options for thermoType for combustion

thermoType

{

type heheuPsiThermo;

mixture inhomogeneousMixture;

transport sutherland;

thermo janaf;

equationOfState perfectGas;

specie specie;

energy absoluteEnthalpy;

//energy absoluteInternalEnergy;

}


engineFoam tutorial

Subsection


Property Type

Thermophysical model heheuPsiThermo

Mixture egrMixture

properties homogeneousMixture

inhomogeneousMixture

veryInhomogeneousMixture

Transport const

properties sutherland

Basic thermophysical hConst

properties janaf

equation of state perfectGas

Derived thermophysical specie

properties

Table: Thermo-physical model


engineFoam tutorial

Subsection


>


engineFoam tutorial

Subsection


Keyword : stoichiometricAirFuelMassRatio

Now for the inhomogeneousMixture it will read the fuel, oxidant andburnt products. Which are defined as follow:

fuel

{

specie

{

nMoles 1;

molWeight 114.23;

}

thermodynamics

{

Tlow 298.15;

Thigh 5000;

Tcommon 1000;

highCpCoeffs (19.3963 0.0488137 -1.55798e-05 2.17831e-09 -1.08391e-13 -37133.9 -78.8531 );

lowCpCoeffs ( 0.429357 0.0765769 8.41306e-06 -5.86603e-08 2.79414e-11 -30446.4 25.6735 );

}

transport

{

As 1.67212e-06;

Ts 170.672;

}

}


engineFoam tutorial

Subsection

constant/combustionProperties

keyword : laminarFlameSpeedCorrelation

1. Gulders

2. GuldersEGR

3. constant

The implementation can be found in:

src/thermophysicalModels/laminarFlameSpeed/Gulders/Gulders.C

src/thermophysicalModels/laminarFlameSpeed/GuldersEGR/GuldersEGR.C

keyword : fuel

keyword : Su

If the laminar flame speed is chosen as constant then it take define value of Su

here.

src/thermophysicalModels/laminarFlameSpeed/constant/constant.C


engineFoam tutorial

Subsection


keyword : equivalenceRatio

It is defined as a ratio of fuel-air ratio to the stoichiometric fuel-air ratio,as:

Su(φ, Tu, pu) = Z W φη e−ξ(φ−σ)2 (TuT0

)α

(pup0

)β

(7)

The values of model constants are also define depending upon the fuelused under the GuldersCoeffs, as:

Propane

{ W 0.446;

eta 0.12;

xi 4.95;

alpha 1.77;

beta -0.2;

f 2.3;

}


engineFoam tutorial

Subsection


keyword : XiModel

1. fixed

2. algebraic

3. transport

Now extented to:

4. muppala

5. zimont


engineFoam tutorial

Subsection


keyword : ignite

ignite yes;

keyword : ignitionSites

{

location (0.03 0 0.091);

diameter 0.002;

start -15;

duration 20;

strength 4;

}


engineFoam tutorial

Subsection

boundary conditions

We have following files in the time folder such as -180 :alphat b epsilon ft fu k mut p Su T Tu U Xi

Variable Description Boundary condition at patches(same at all the patches except moving patch)

alphat Thermal diffusivity type compressible::alphatWallFunction;Prt 0.85;value uniform 0;

b Regression variable zeroGradient;epsilon Turbulent kinetic type compressible::epsilonWallFunction;

energy dissipation Cmu 0.09;rate kappa 0.41;

E 9.8;value uniform 450;

k Turbulent kinetic energy type compressible::kqRWallFunction;value uniform 4;

mut Turbulent viscosity type mutkWallFunction;Cmu 0.09;kappa 0.41;E 9.8;value uniform 0;


engineFoam tutorial

Subsection

boundary conditions

p pressure zeroGradientSu laminar flame speed zeroGradientT burnt fixed value

Temperature uniform 433;Tu unburnt fixed value

Temperature uniform 433;U velocity fixed value

uniform (0 0 0);Xi flame wrinkling zeroGradient

Run the simulation :

./Allclean

./Allrun > log 2>&1 &


engineFoam tutorial

Subsection

Results

Qualitative comparison

>

Figure: Regression variable (b) at 0 crank angle degree.


engineFoam tutorial

Subsection

Results

Quantitative comparison

Figure: In-cylinder pressure (left) and temperature (right).


engineFoam tutorial

Subsection

Thanks for you attention!


Documents

engineFoam tutorial with different flame-wrinkling (Xi) modelhani/kurser/OS_CFD_2018/SandipWadekar/sli… · Sandip Wadekar Mechanics and Maritime Sciences, Chalmers University of