setRDeltaT.H

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{
    volScalarField& rDeltaT = trDeltaT.ref();

    const dictionary& pimpleDict = pimple.dict();

    scalar maxCo
    (
        pimpleDict.getOrDefault<scalar>("maxCo", 0.9)
    );

    scalar maxAlphaCo
    (
        pimpleDict.getOrDefault<scalar>("maxAlphaCo", 0.2)
    );

    scalar rDeltaTSmoothingCoeff
    (
        pimpleDict.getOrDefault<scalar>("rDeltaTSmoothingCoeff", 0.1)
    );

    label nAlphaSpreadIter
    (
        pimpleDict.getOrDefault<label>("nAlphaSpreadIter", 1)
    );

    scalar alphaSpreadDiff
    (
        pimpleDict.getOrDefault<scalar>("alphaSpreadDiff", 0.2)
    );

    scalar alphaSpreadMax
    (
        pimpleDict.getOrDefault<scalar>("alphaSpreadMax", 0.99)
    );

    scalar alphaSpreadMin
    (
        pimpleDict.getOrDefault<scalar>("alphaSpreadMin", 0.01)
    );

    label nAlphaSweepIter
    (
        pimpleDict.getOrDefault<label>("nAlphaSweepIter", 5)
    );

    scalar rDeltaTDampingCoeff
    (
        pimpleDict.getOrDefault<scalar>("rDeltaTDampingCoeff", 1.0)
    );

    scalar maxDeltaT
    (
        pimpleDict.getOrDefault<scalar>("maxDeltaT", GREAT)
    );


    // The old reciprocal time scale field, with any damping factor
    tmp<volScalarField> rDeltaT0_damped;

    // Calculate damped value before applying any other changes
    if
    (
        rDeltaTDampingCoeff < 1
     && runTime.timeIndex() > runTime.startTimeIndex() + 1
    )
    {
        rDeltaT0_damped = (scalar(1) - rDeltaTDampingCoeff)*(rDeltaT);
    }


    volScalarField rDeltaT0("rDeltaT0", rDeltaT);

    // Set the reciprocal time-step from the local Courant number
    rDeltaT.ref() = max
    (
        1/dimensionedScalar("maxDeltaT", dimTime, maxDeltaT),
        fvc::surfaceSum(mag(rhoPhi))()()
       /((2*maxCo)*mesh.V()*rho())
    );

    if (maxAlphaCo < maxCo)
    {
        // Further limit the reciprocal time-step
        // in the vicinity of the interface

        volScalarField alpha1Bar(fvc::average(alpha1));

        rDeltaT.ref() = max
        (
            rDeltaT(),
            pos0(alpha1Bar() - alphaSpreadMin)
           *pos0(alphaSpreadMax - alpha1Bar())
           *fvc::surfaceSum(mag(phi))()()
           /((2*maxAlphaCo)*mesh.V())
        );
    }

    // Update tho boundary values of the reciprocal time-step
    rDeltaT.correctBoundaryConditions();

    {
        auto limits = gMinMax(rDeltaT.primitiveField());
        limits.reset(1/(limits.max()+VSMALL), 1/(limits.min()+VSMALL));

        Info<< "Flow time scale min/max = "
            << limits.min() << ", " << limits.max() << endl;
    }
    if (rDeltaTSmoothingCoeff < 1.0)
    {
        fvc::smooth(rDeltaT, rDeltaTSmoothingCoeff);
    }

    if (nAlphaSpreadIter > 0)
    {
        fvc::spread
        (
            rDeltaT,
            alpha1,
            nAlphaSpreadIter,
            alphaSpreadDiff,
            alphaSpreadMax,
            alphaSpreadMin
        );
    }

    if (nAlphaSweepIter > 0)
    {
        fvc::sweep(rDeltaT, alpha1, nAlphaSweepIter, alphaSpreadDiff);
    }

    {
        auto limits = gMinMax(rDeltaT.primitiveField());
        limits.reset(1/(limits.max()+VSMALL), 1/(limits.min()+VSMALL));

        Info<< "Smoothed flow time scale min/max = "
            << limits.min() << ", " << limits.max() << endl;
    }

    // Limit rate of change of time scale (=> smallest reciprocal time)
    // - reduce as much as required
    // - only increase at a fraction of old time scale
    if (rDeltaT0_damped)
    {
        rDeltaT.clamp_min(rDeltaT0_damped());

        auto limits = gMinMax(rDeltaT.primitiveField());
        limits.reset(1/(limits.max()+VSMALL), 1/(limits.min()+VSMALL));

        Info<< "Damped flow time scale min/max = "
            << limits.min() << ", " << limits.max() << endl;
    }
}