interfaceProperties.C

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    Copyright (C) 2022 OpenCFD Ltd.
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    This file is part of OpenFOAM.
 
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#include "interfaceProperties.H"
#include "alphaContactAngleTwoPhaseFvPatchScalarField.H"
#include "mathematicalConstants.H"
#include "surfaceInterpolate.H"
#include "fvcDiv.H"
#include "fvcGrad.H"
#include "fvcSnGrad.H"
#include "fvcAverage.H"
#include "unitConversion.H"
 
// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
// Correction for the boundary condition on the unit normal nHat on
// walls to produce the correct contact angle.
 
// The dynamic contact angle is calculated from the component of the
// velocity on the direction of the interface, parallel to the wall.
 
void Foam::interfaceProperties::correctContactAngle
(
    surfaceVectorField::Boundary& nHatb,
    const surfaceVectorField::Boundary& gradAlphaf
) const
{
    const fvMesh& mesh = alpha1_.mesh();
    const volScalarField::Boundary& abf = alpha1_.boundaryField();
 
    const fvBoundaryMesh& boundary = mesh.boundary();
 
    forAll(boundary, patchi)
    {
        if (isA<alphaContactAngleTwoPhaseFvPatchScalarField>(abf[patchi]))
        {
            alphaContactAngleTwoPhaseFvPatchScalarField& acap =
                const_cast<alphaContactAngleTwoPhaseFvPatchScalarField&>
                (
                    refCast<const alphaContactAngleTwoPhaseFvPatchScalarField>
                    (
                        abf[patchi]
                    )
                );
 
            fvsPatchVectorField& nHatp = nHatb[patchi];
            const scalarField theta
            (
                degToRad() * acap.theta(U_.boundaryField()[patchi], nHatp)
            );
 
            const vectorField nf
            (
                boundary[patchi].nf()
            );
 
            // Reset nHatp to correspond to the contact angle
 
            const scalarField a12(nHatp & nf);
            const scalarField b1(cos(theta));
 
            scalarField b2(nHatp.size());
            forAll(b2, facei)
            {
                b2[facei] = cos(acos(a12[facei]) - theta[facei]);
            }
 
            const scalarField det(1.0 - a12*a12);
 
            scalarField a((b1 - a12*b2)/det);
            scalarField b((b2 - a12*b1)/det);
 
            nHatp = a*nf + b*nHatp;
            nHatp /= (mag(nHatp) + deltaN_.value());
 
            acap.gradient() = (nf & nHatp)*mag(gradAlphaf[patchi]);
            acap.evaluate();
        }
    }
}
 
 
void Foam::interfaceProperties::calculateK()
{
    const fvMesh& mesh = alpha1_.mesh();
    const surfaceVectorField& Sf = mesh.Sf();
 
    // Cell gradient of alpha
    tmp<volVectorField> tgradAlpha;
    if (nAlphaSmoothCurvature_ < 1)
    {
        tgradAlpha = fvc::grad(alpha1_, "nHat");
    }
    else
    {
        // Smooth interface curvature to reduce spurious currents
        auto talpha1L = tmp<volScalarField>::New(alpha1_);
        auto& alpha1L = talpha1L.ref();
 
        for (int i = 0; i < nAlphaSmoothCurvature_; ++i)
        {
            alpha1L = fvc::average(fvc::interpolate(alpha1L));
        }
 
        tgradAlpha = fvc::grad(talpha1L, "nHat");
    }
 
    // Interpolated face-gradient of alpha
    surfaceVectorField gradAlphaf(fvc::interpolate(tgradAlpha));
 
    //gradAlphaf -=
    //    (mesh.Sf()/mesh.magSf())
    //   *(fvc::snGrad(alpha1_) - (mesh.Sf() & gradAlphaf)/mesh.magSf());
 
    // Face unit interface normal
    surfaceVectorField nHatfv(gradAlphaf/(mag(gradAlphaf) + deltaN_));
    // surfaceVectorField nHatfv
    // (
    //     (gradAlphaf + deltaN_*vector(0, 0, 1)
    //    *sign(gradAlphaf.component(vector::Z)))/(mag(gradAlphaf) + deltaN_)
    // );
    correctContactAngle(nHatfv.boundaryFieldRef(), gradAlphaf.boundaryField());
 
    // Face unit interface normal flux
    nHatf_ = nHatfv & Sf;
 
    // Simple expression for curvature
    K_ = -fvc::div(nHatf_);
 
    // Complex expression for curvature.
    // Correction is formally zero but numerically non-zero.
    /*
    volVectorField nHat(gradAlpha/(mag(gradAlpha) + deltaN_));
    forAll(nHat.boundaryField(), patchi)
    {
        nHat.boundaryFieldRef()[patchi] = nHatfv.boundaryField()[patchi];
    }
 
    K_ = -fvc::div(nHatf_) + (nHat & fvc::grad(nHatfv) & nHat);
    */
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
Foam::interfaceProperties::interfaceProperties
(
    const volScalarField& alpha1,
    const volVectorField& U,
    const IOdictionary& dict
)
:
    transportPropertiesDict_(dict),
    nAlphaSmoothCurvature_
    (
        alpha1.mesh().solverDict(alpha1.name()).
            getOrDefault<int>("nAlphaSmoothCurvature", 0)
    ),
    cAlpha_
    (
        alpha1.mesh().solverDict(alpha1.name()).get<scalar>("cAlpha")
    ),
 
    sigmaPtr_(surfaceTensionModel::New(dict, alpha1.mesh())),
 
    deltaN_
    (
        "deltaN",
        1e-8/cbrt(average(alpha1.mesh().V()))
    ),
 
    alpha1_(alpha1),
    U_(U),
 
    nHatf_
    (
        IOobject
        (
            "nHatf",
            alpha1_.time().timeName(),
            alpha1_.mesh()
        ),
        alpha1_.mesh(),
        dimensionedScalar(dimArea, Zero)
    ),
 
    K_
    (
        IOobject
        (
            "interfaceProperties:K",
            alpha1_.time().timeName(),
            alpha1_.mesh()
        ),
        alpha1_.mesh(),
        dimensionedScalar(dimless/dimLength, Zero)
    )
{
    calculateK();
}
 
 
// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
Foam::tmp<Foam::volScalarField>
Foam::interfaceProperties::sigmaK() const
{
    return sigmaPtr_->sigma()*K_;
}
 
 
Foam::tmp<Foam::surfaceScalarField>
Foam::interfaceProperties::surfaceTensionForce() const
{
    return fvc::interpolate(sigmaK())*fvc::snGrad(alpha1_);
}
 
 
Foam::tmp<Foam::volScalarField>
Foam::interfaceProperties::nearInterface() const
{
    return pos0(alpha1_ - 0.01)*pos0(0.99 - alpha1_);
}
 
 
void Foam::interfaceProperties::correct()
{
    calculateK();
}
 
 
bool Foam::interfaceProperties::read()
{
    alpha1_.mesh().solverDict(alpha1_.name()).readEntry("cAlpha", cAlpha_);
    sigmaPtr_->readDict(transportPropertiesDict_);
 
    return true;
}
 
 
// ************************************************************************* //