filteredLinear2.H

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/*---------------------------------------------------------------------------*\
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License
    This file is part of OpenFOAM.

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Class
    Foam::filteredLinear2Limiter

Description
    Class to generate weighting factors for the filteredLinear2
    differencing scheme.

    The aim is to remove high-frequency modes with "staggering"
    characteristics by comparing the face gradient with both neighbouring
    cell gradients and introduce small amounts of upwind in order to damp
    these modes.

    Used in conjunction with the template class LimitedScheme.

SourceFiles
    filteredLinear2.C

\*---------------------------------------------------------------------------*/

#ifndef filteredLinear2_H
#define filteredLinear2_H

#include <OpenFOAM/vector.H>

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

namespace Foam
{

/*---------------------------------------------------------------------------*\
                     Class filteredLinear2Limiter Declaration
\*---------------------------------------------------------------------------*/

template<class LimiterFunc>
class filteredLinear2Limiter
:
    public LimiterFunc
{
    // Private data

        // Scaling corefficient for the gradient ratio,
        // 0 = linear
        // 1 = fully limited
        scalar k_;

        // Maximum allowed overshoot/undershoot relative to the difference
        // across the face.
        // On input:
        //     0 = no overshoot/undershoot
        //     1 = overshoot/undershoot equal to the difference across the face
        // Note: After input 1 is added to l_
        scalar l_;


public:

    filteredLinear2Limiter(Istream& is)
    :
        k_(readScalar(is)),
        l_(readScalar(is))
    {
        if (k_ < 0 || k_ > 1)
        {
            FatalIOErrorIn("filteredLinearV2Limiter(Istream& is)", is)
                << "coefficient = " << k_
                << " should be >= 0 and <= 1"
                << exit(FatalIOError);
        }

        if (l_ < 0 || l_ > 1)
        {
            FatalIOErrorIn("filteredLinearV2Limiter(Istream& is)", is)
                << "coefficient = " << l_
                << " should be >= 0 and <= 1"
                << exit(FatalIOError);
        }

        l_ += 1.0;
    }

    scalar limiter
    (
        const scalar cdWeight,
        const scalar faceFlux,
        const typename LimiterFunc::phiType& phiP,
        const typename LimiterFunc::phiType& phiN,
        const typename LimiterFunc::gradPhiType& gradcP,
        const typename LimiterFunc::gradPhiType& gradcN,
        const vector& d
    ) const
    {
        // Difference across face
        scalar df = phiN - phiP;

        // Twice the differences across face-neighbour cells
        scalar tdcP = 2*(d & gradcP);
        scalar tdcN = 2*(d & gradcN);

        // Calculate the limiter according to the sign of the face difference
        scalar limiter;

        if (df > 0)
        {
            limiter = l_
                - k_*min(max(df - tdcP, 0), max(df - tdcN, 0))
                /(max(mag(df), max(mag(tdcP), mag(tdcN))) + SMALL);
        }
        else
        {
            limiter = l_
                - k_*min(max(tdcP - df, 0), max(tdcN - df, 0))
                /(max(mag(df), max(mag(tdcP), mag(tdcN))) + SMALL);
        }

        // Limit the limiter between linear and upwind
        return max(min(limiter, 1), 0);
    }
};


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

} // End namespace Foam

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

#endif

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