kEpsilon.C

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    Copyright (C) 2019-2023 OpenCFD Ltd.
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#include "kEpsilon.H"
#include "fvOptions.H"
#include "bound.H"
#include "wallDist.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
namespace RASModels
{
 
// * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
 
template<class BasicTurbulenceModel>
void kEpsilon<BasicTurbulenceModel>::correctNut()
{
    this->nut_ = Cmu_*sqr(k_)/epsilon_;
 
    if (twoLayerTreatment_)
    {
        const volScalarField& y = wallDist::New(this->mesh_).y();
 
        // Using the TKE of previous time-step to freeze the turbulent Reynolds
        // number during the current time-step and hence freeze the separation
        // of inner and outer layer.
        const volScalarField Rey(mag(y*sqrt(k_.oldTime())/this->nu()));
 
        const dimensionedScalar ClStar(0.41*pow(Cmu_, -0.75));
        auto& lEps = *lEpsPtr_;
        lEps = y*ClStar*(1.0 - exp(-1.0*Rey/(2*ClStar)));
 
        const dimensionedScalar A(ReyFactor_*ReyStar_/atanh(0.98));
        auto& lambdaEps = *lambdaEpsPtr_;
        lambdaEps = 0.5*(1.0 + tanh((Rey - ReyStar_)/A));
 
        // High-Re part
        this->nut_ *= lambdaEps;
 
        // Low-Re part
        const scalar Amu = 70.0;
        const volScalarField lMu(y*ClStar*(1.0 - exp(-1.0*Rey/Amu)));
        this->nut_ += (1.0-lambdaEps)*Cmu_*lMu*sqrt(k_);
    }
 
    this->nut_.correctBoundaryConditions();
    fv::options::New(this->mesh_).correct(this->nut_);
 
    BasicTurbulenceModel::correctNut();
}
 
 
template<class BasicTurbulenceModel>
tmp<fvScalarMatrix> kEpsilon<BasicTurbulenceModel>::kSource() const
{
    // Source term for k equation (added to RHS)
 
    if (twoLayerTreatment_)
    {
        // Local references
        const alphaField& alpha = this->alpha_;
        const rhoField& rho = this->rho_;
        const volScalarField::Internal& lEps = *lEpsPtr_;
        const volScalarField& lambdaEps = *lambdaEpsPtr_;
 
        return
           -fvm::Sp
            (
                alpha()*rho()*(1.0-lambdaEps())
               *(sqrt(k_())/lEps - epsilon_()/k_()),
                k_
            );
    }
 
    return tmp<fvScalarMatrix>::New
    (
        k_,
        dimVolume*this->rho_.dimensions()*k_.dimensions()/dimTime
    );
}
 
 
template<class BasicTurbulenceModel>
tmp<fvScalarMatrix> kEpsilon<BasicTurbulenceModel>::epsilonSource() const
{
    return tmp<fvScalarMatrix>::New
    (
        epsilon_,
        dimVolume*this->rho_.dimensions()*epsilon_.dimensions()/dimTime
    );
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
template<class BasicTurbulenceModel>
kEpsilon<BasicTurbulenceModel>::kEpsilon
(
    const alphaField& alpha,
    const rhoField& rho,
    const volVectorField& U,
    const surfaceScalarField& alphaRhoPhi,
    const surfaceScalarField& phi,
    const transportModel& transport,
    const word& propertiesName,
    const word& type
)
:
    eddyViscosity<RASModel<BasicTurbulenceModel>>
    (
        type,
        alpha,
        rho,
        U,
        alphaRhoPhi,
        phi,
        transport,
        propertiesName
    ),
 
    Cmu_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "Cmu",
            this->coeffDict_,
            0.09
        )
    ),
    C1_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "C1",
            this->coeffDict_,
            1.44
        )
    ),
    C2_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "C2",
            this->coeffDict_,
            1.92
        )
    ),
    C3_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "C3",
            this->coeffDict_,
            0
        )
    ),
    sigmak_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "sigmak",
            this->coeffDict_,
            1.0
        )
    ),
    sigmaEps_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "sigmaEps",
            this->coeffDict_,
            1.3
        )
    ),
    k_
    (
        IOobject
        (
            IOobject::groupName("k", alphaRhoPhi.group()),
            this->runTime_.timeName(),
            this->mesh_,
            IOobject::MUST_READ,
            IOobject::AUTO_WRITE
        ),
        this->mesh_
    ),
    epsilon_
    (
        IOobject
        (
            IOobject::groupName("epsilon", alphaRhoPhi.group()),
            this->runTime_.timeName(),
            this->mesh_,
            IOobject::MUST_READ,
            IOobject::AUTO_WRITE
        ),
        this->mesh_
    ),
    twoLayerTreatment_
    (
        Switch::getOrAddToDict
        (
            "twoLayerTreatment",
            this->coeffDict_,
            false
        )
    ),
    ReyStar_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "ReyStar",
            this->coeffDict_,
            200.0
        )
    ),
    ReyFactor_
    (
        dimensioned<scalar>::getOrAddToDict
        (
            "ReyFactor",
            this->coeffDict_,
            0.05
        )
    )
{
    if (twoLayerTreatment_)
    {
        Info<< "Two-layer wall treatment activated" << endl;
 
        lEpsPtr_ = std::make_unique<volScalarField::Internal>
        (
            IOobject
            (
                "lEps",
                this->runTime_.name(),
                this->mesh_,
                IOobject::READ_IF_PRESENT,
                IOobject::AUTO_WRITE
            ),
            this->mesh_,
            dimensionedScalar(dimLength, Zero)
        );
 
        lambdaEpsPtr_ = std::make_unique<volScalarField>
        (
            IOobject
            (
                "lambdaEps",
                this->runTime_.name(),
                this->mesh_,
                IOobject::READ_IF_PRESENT,
                IOobject::AUTO_WRITE
            ),
            this->mesh_,
            dimensionedScalar("lambdaEps", dimless, 1.0)
        );
    }
 
    bound(k_, this->kMin_);
    bound(epsilon_, this->epsilonMin_);
 
    if (type == typeName)
    {
        this->printCoeffs(type);
    }
}
 
 
// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
template<class BasicTurbulenceModel>
bool kEpsilon<BasicTurbulenceModel>::read()
{
    if (eddyViscosity<RASModel<BasicTurbulenceModel>>::read())
    {
        Cmu_.readIfPresent(this->coeffDict());
        C1_.readIfPresent(this->coeffDict());
        C2_.readIfPresent(this->coeffDict());
        C3_.readIfPresent(this->coeffDict());
        sigmak_.readIfPresent(this->coeffDict());
        sigmaEps_.readIfPresent(this->coeffDict());
 
        // Two-layer wall treatment
        // Note: these are the only parameters that can be changed at runtime
        ReyStar_.readIfPresent(this->coeffDict());
        ReyFactor_.readIfPresent(this->coeffDict());
 
        return true;
    }
 
    return false;
}
 
 
template<class BasicTurbulenceModel>
void kEpsilon<BasicTurbulenceModel>::correct()
{
    if (!this->turbulence_)
    {
        return;
    }
 
    // Local references
    const alphaField& alpha = this->alpha_;
    const rhoField& rho = this->rho_;
    const surfaceScalarField& alphaRhoPhi = this->alphaRhoPhi_;
    const volVectorField& U = this->U_;
    const volScalarField& nut = this->nut_;
 
    fv::options& fvOptions(fv::options::New(this->mesh_));
 
    eddyViscosity<RASModel<BasicTurbulenceModel>>::correct();
 
    const volScalarField::Internal divU
    (
        fvc::div(fvc::absolute(this->phi(), U))().v()
    );
 
    tmp<volTensorField> tgradU = fvc::grad(U);
    const volScalarField::Internal GbyNu
    (
        IOobject::scopedName(this->type(), "GbyNu"),
        tgradU().v() && devTwoSymm(tgradU().v())
    );
    const volScalarField::Internal G(this->GName(), nut()*GbyNu);
    tgradU.clear();
 
    // Update epsilon and G at the wall
    epsilon_.boundaryFieldRef().updateCoeffs();
    // Push any changed cell values to coupled neighbours
    epsilon_.boundaryFieldRef().template evaluateCoupled<coupledFvPatch>();
 
    // Dissipation equation
    tmp<fvScalarMatrix> epsEqn
    (
        fvm::ddt(alpha, rho, epsilon_)
      + fvm::div(alphaRhoPhi, epsilon_)
      - fvm::laplacian(alpha*rho*DepsilonEff(), epsilon_)
     ==
        C1_*alpha()*rho()*GbyNu*Cmu_*k_()
      - fvm::SuSp(((2.0/3.0)*C1_ - C3_)*alpha()*rho()*divU, epsilon_)
      - fvm::Sp(C2_*alpha()*rho()*epsilon_()/k_(), epsilon_)
      + epsilonSource()
      + fvOptions(alpha, rho, epsilon_)
    );
 
    epsEqn.ref().relax();
    fvOptions.constrain(epsEqn.ref());
    epsEqn.ref().boundaryManipulate(epsilon_.boundaryFieldRef());
    solve(epsEqn);
    fvOptions.correct(epsilon_);
    bound(epsilon_, this->epsilonMin_);
 
    // Turbulent kinetic energy equation
    tmp<fvScalarMatrix> kEqn
    (
        fvm::ddt(alpha, rho, k_)
      + fvm::div(alphaRhoPhi, k_)
      - fvm::laplacian(alpha*rho*DkEff(), k_)
     ==
        alpha()*rho()*G
      - fvm::SuSp((2.0/3.0)*alpha()*rho()*divU, k_)
      - fvm::Sp(alpha()*rho()*epsilon_()/k_(), k_)
      + kSource()
      + fvOptions(alpha, rho, k_)
    );
 
    kEqn.ref().relax();
    fvOptions.constrain(kEqn.ref());
    solve(kEqn);
    fvOptions.correct(k_);
    bound(k_, this->kMin_);
 
    correctNut();
}
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
} // End namespace RASModels
} // End namespace Foam
 
// ************************************************************************* //