alphaPredictor.C

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-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.
 
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    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.
 
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#include "twoPhaseSolver.H"
#include "subCycle.H"
#include "interfaceCompression.H"
#include "CMULES.H"
#include "CrankNicolsonDdtScheme.H"
#include "fvcFlux.H"
#include "fvmSup.H"
 
// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
Foam::tmp<Foam::surfaceScalarField> Foam::solvers::twoPhaseSolver::alphaPhi
(
    const surfaceScalarField& phi,
    const volScalarField& alpha,
    const dictionary& alphaControls
)
{
    const word alphaScheme(mesh.schemes().div(divAlphaName)[1].wordToken());
 
    ITstream compressionScheme
    (
        compressionSchemes.found(alphaScheme)
      ? mesh.schemes().div(divAlphaName)
      : ITstream
        (
            divAlphaName,
            tokenList
            {
                word("Gauss"),
                word("interfaceCompression"),
                alphaScheme,
                alphaControls.lookup<scalar>("cAlpha")
            }
        )
    );
 
    return fvc::flux
    (
        phi,
        alpha,
        compressionScheme
    );
}
 
 
void Foam::solvers::twoPhaseSolver::alphaSolve
(
    const dictionary& alphaControls
)
{
    const label nAlphaSubCycles(alphaControls.lookup<label>("nAlphaSubCycles"));
 
    const label nAlphaCorr(alphaControls.lookup<label>("nAlphaCorr"));
 
    const bool MULESCorr
    (
        alphaControls.lookupOrDefault<Switch>("MULESCorr", false)
    );
 
    // Apply the compression correction from the previous iteration
    // Improves efficiency for steady-simulations but can only be applied
    // once the alpha field is reasonably steady, i.e. fully developed
    const bool alphaApplyPrevCorr
    (
        alphaControls.lookupOrDefault<Switch>("alphaApplyPrevCorr", false)
    );
 
 
    // Set the off-centering coefficient according to ddt scheme
    scalar ocCoeff = 0;
    {
        tmp<fv::ddtScheme<scalar>> tddtAlpha
        (
            fv::ddtScheme<scalar>::New
            (
                mesh,
                mesh.schemes().ddt("ddt(alpha)")
            )
        );
        const fv::ddtScheme<scalar>& ddtAlpha = tddtAlpha();
 
        if
        (
            isType<fv::EulerDdtScheme<scalar>>(ddtAlpha)
         || isType<fv::localEulerDdtScheme<scalar>>(ddtAlpha)
        )
        {
            ocCoeff = 0;
        }
        else if (isType<fv::CrankNicolsonDdtScheme<scalar>>(ddtAlpha))
        {
            if (nAlphaSubCycles > 1)
            {
                FatalErrorInFunction
                    << "Sub-cycling is not supported "
                       "with the CrankNicolson ddt scheme"
                    << exit(FatalError);
            }
 
            if
            (
                alphaRestart
             || mesh.time().timeIndex() > mesh.time().startTimeIndex() + 1
            )
            {
                ocCoeff =
                    refCast<const fv::CrankNicolsonDdtScheme<scalar>>(ddtAlpha)
                   .ocCoeff();
            }
        }
        else
        {
            FatalErrorInFunction
                << "Only Euler and CrankNicolson ddt schemes are supported"
                << exit(FatalError);
        }
    }
 
    // Set the time blending factor, 1 for Euler
    scalar cnCoeff = 1.0/(1.0 + ocCoeff);
 
    tmp<surfaceScalarField> phiCN(phi);
 
    // Calculate the Crank-Nicolson off-centred volumetric flux
    if (ocCoeff > 0)
    {
        phiCN = surfaceScalarField::New
        (
            "phiCN",
            cnCoeff*phi + (1.0 - cnCoeff)*phi.oldTime()
        );
    }
 
    tmp<volScalarField> divU;
 
    if (divergent())
    {
        divU =
        (
            mesh.moving()
          ? fvc::div(phiCN() + mesh.phi())
          : fvc::div(phiCN())
        );
    }
 
    tmp<volScalarField::Internal> Su;
    tmp<volScalarField::Internal> Sp;
 
    alphaSuSp(Su, Sp);
 
    if (MULESCorr)
    {
        fvScalarMatrix alpha1Eqn
        (
            (
                LTS
              ? fv::localEulerDdtScheme<scalar>(mesh).fvmDdt(alpha1)
              : fv::EulerDdtScheme<scalar>(mesh).fvmDdt(alpha1)
            )
          + fv::gaussConvectionScheme<scalar>
            (
                mesh,
                phiCN,
                upwind<scalar>(mesh, phiCN)
            ).fvmDiv(phiCN, alpha1)
        );
 
        if (divU.valid())
        {
            alpha1Eqn -= Su() + fvm::Sp(Sp() + divU(), alpha1);
        }
 
        alpha1Eqn.solve();
 
        Info<< "Phase-1 volume fraction = "
            << alpha1.weightedAverage(mesh.Vsc()).value()
            << "  Min(" << alpha1.name() << ") = " << min(alpha1).value()
            << "  Max(" << alpha1.name() << ") = " << max(alpha1).value()
            << endl;
 
        tmp<surfaceScalarField> talphaPhi1UD(alpha1Eqn.flux());
        alphaPhi1 = talphaPhi1UD();
 
        if (alphaApplyPrevCorr && talphaPhi1Corr0.valid())
        {
            Info<< "Applying the previous iteration compression flux" << endl;
            MULES::correct
            (
                geometricOneField(),
                alpha1,
                alphaPhi1,
                talphaPhi1Corr0.ref(),
                oneField(),
                zeroField()
            );
 
            alphaPhi1 += talphaPhi1Corr0();
        }
 
        // Cache the upwind-flux
        talphaPhi1Corr0 = talphaPhi1UD;
 
        alpha2 = 1.0 - alpha1;
 
        correctInterface();
    }
 
    for (int aCorr=0; aCorr<nAlphaCorr; aCorr++)
    {
        // Split operator
        tmp<surfaceScalarField> talphaPhi1Un
        (
            alphaPhi
            (
                phiCN(),
                (cnCoeff*alpha1 + (1.0 - cnCoeff)*alpha1.oldTime())(),
                alphaControls
            )
        );
 
        if (MULESCorr)
        {
            tmp<surfaceScalarField> talphaPhi1Corr(talphaPhi1Un() - alphaPhi1);
            volScalarField alpha10("alpha10", alpha1);
 
            if (divU.valid())
            {
                MULES::correct
                (
                    geometricOneField(),
                    alpha1,
                    talphaPhi1Un(),
                    talphaPhi1Corr.ref(),
                    Sp(),
                    (-Sp()*alpha1)(),
                    oneField(),
                    zeroField()
                );
            }
            else
            {
                MULES::correct
                (
                    geometricOneField(),
                    alpha1,
                    talphaPhi1Un(),
                    talphaPhi1Corr.ref(),
                    oneField(),
                    zeroField()
                );
            }
 
            // Under-relax the correction for all but the 1st corrector
            if (aCorr == 0)
            {
                alphaPhi1 += talphaPhi1Corr();
            }
            else
            {
                alpha1 = 0.5*alpha1 + 0.5*alpha10;
                alphaPhi1 += 0.5*talphaPhi1Corr();
            }
        }
        else
        {
            alphaPhi1 = talphaPhi1Un;
 
            if (divU.valid())
            {
                MULES::explicitSolve
                (
                    geometricOneField(),
                    alpha1,
                    phiCN,
                    alphaPhi1,
                    Sp(),
                    (Su() + divU()*min(alpha1(), scalar(1)))(),
                    oneField(),
                    zeroField()
                );
            }
            else
            {
                MULES::explicitSolve
                (
                    geometricOneField(),
                    alpha1,
                    phiCN,
                    alphaPhi1,
                    oneField(),
                    zeroField()
                );
            }
        }
 
        alpha2 = 1.0 - alpha1;
 
        // Correct only the mixture interface for the interface compression flux
        correctInterface();
    }
 
    if (alphaApplyPrevCorr && MULESCorr)
    {
        talphaPhi1Corr0 = alphaPhi1 - talphaPhi1Corr0;
 
        // Register alphaPhiCorr0.<phase1> for redistribution
        talphaPhi1Corr0.ref().rename
        (
            IOobject::groupName("alphaPhiCorr0", alpha1.group())
        );
        talphaPhi1Corr0.ref().checkIn();
    }
    else
    {
        talphaPhi1Corr0.clear();
    }
 
    if
    (
        word(mesh.schemes().ddt("ddt(rho,U)"))
     != fv::EulerDdtScheme<vector>::typeName
     && word(mesh.schemes().ddt("ddt(rho,U)"))
     != fv::localEulerDdtScheme<vector>::typeName
    )
    {
        if (ocCoeff > 0)
        {
            // Calculate the end-of-time-step alpha flux
            alphaPhi1 =
                (alphaPhi1 - (1.0 - cnCoeff)*alphaPhi1.oldTime())/cnCoeff;
        }
    }
 
    Info<< "Phase-1 volume fraction = "
        << alpha1.weightedAverage(mesh.Vsc()).value()
        << "  Min(" << alpha1.name() << ") = " << min(alpha1).value()
        << "  Max(" << alpha1.name() << ") = " << max(alpha1).value()
        << endl;
}
 
 
void Foam::solvers::twoPhaseSolver::alphaPredictor()
{
    const dictionary& alphaControls = mesh.solution().solverDict(alpha1.name());
 
    const label nAlphaSubCycles(alphaControls.lookup<label>("nAlphaSubCycles"));
 
 
    if (nAlphaSubCycles > 1)
    {
        dimensionedScalar totalDeltaT = runTime.deltaT();
        tmp<volScalarField> trSubDeltaT;
 
        if (LTS)
        {
            trSubDeltaT =
                fv::localEulerDdt::localRSubDeltaT(mesh, nAlphaSubCycles);
        }
 
        // Create a temporary alphaPhi1 to accumulate the sub-cycled alphaPhi1
        tmp<surfaceScalarField> talphaPhi1
        (
            surfaceScalarField::New
            (
                "alphaPhi1",
                mesh,
                dimensionedScalar(alphaPhi1.dimensions(), 0)
            )
        );
 
        List<volScalarField*> alphaPtrs({&alpha1, &alpha2});
 
        for
        (
            subCycle<volScalarField, subCycleFields> alphaSubCycle
            (
                alphaPtrs,
                nAlphaSubCycles
            );
            !(++alphaSubCycle).end();
        )
        {
            alphaSolve(alphaControls);
            talphaPhi1.ref() += (runTime.deltaT()/totalDeltaT)*alphaPhi1;
        }
 
        alphaPhi1 = talphaPhi1();
    }
    else
    {
        alphaSolve(alphaControls);
    }
}
 
 
// ************************************************************************* //