threePhaseInterfaceProperties.C

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Application
    threePhaseInterfaceProperties

Description
    Properties to aid interFoam :
    1. Correct the alpha boundary condition for dynamic contact angle.
    2. Calculate interface curvature.

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

#include "threePhaseInterfaceProperties.H"
#include <twoPhaseInterfaceProperties/alphaContactAngleFvPatchScalarField.H>
#include <OpenFOAM/mathematicalConstants.H>
#include <finiteVolume/surfaceInterpolate.H>
#include <finiteVolume/fvcDiv.H>
#include <finiteVolume/fvcGrad.H>

// * * * * * * * * * * * * * * * Static Member Data  * * * * * * * * * * * * //

const Foam::scalar Foam::threePhaseInterfaceProperties::convertToRad =
    Foam::mathematicalConstant::pi/180.0;


// * * * * * * * * * * * * * 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::threePhaseInterfaceProperties::correctContactAngle
(
    surfaceVectorField::GeometricBoundaryField& nHatb
) const
{
    const volScalarField::GeometricBoundaryField& alpha1 =
        mixture_.alpha1().boundaryField();
    const volScalarField::GeometricBoundaryField& alpha2 =
        mixture_.alpha2().boundaryField();
    const volScalarField::GeometricBoundaryField& alpha3 =
        mixture_.alpha3().boundaryField();
    const volVectorField::GeometricBoundaryField& U =
        mixture_.U().boundaryField();

    const fvMesh& mesh = mixture_.U().mesh();
    const fvBoundaryMesh& boundary = mesh.boundary();

    forAll(boundary, patchi)
    {
        if (isA<alphaContactAngleFvPatchScalarField>(alpha1[patchi]))
        {
            const alphaContactAngleFvPatchScalarField& a2cap =
                refCast<const alphaContactAngleFvPatchScalarField>
                (alpha2[patchi]);

            const alphaContactAngleFvPatchScalarField& a3cap =
                refCast<const alphaContactAngleFvPatchScalarField>
                (alpha3[patchi]);

            scalarField twoPhaseAlpha2 = max(a2cap, scalar(0));
            scalarField twoPhaseAlpha3 = max(a3cap, scalar(0));

            scalarField sumTwoPhaseAlpha =
                twoPhaseAlpha2 + twoPhaseAlpha3 + SMALL;

            twoPhaseAlpha2 /= sumTwoPhaseAlpha;
            twoPhaseAlpha3 /= sumTwoPhaseAlpha;

            fvsPatchVectorField& nHatp = nHatb[patchi];

            scalarField theta =
                convertToRad
               *(
                   twoPhaseAlpha2*(180 - a2cap.theta(U[patchi], nHatp))
                 + twoPhaseAlpha3*(180 - a3cap.theta(U[patchi], nHatp))
               );

            vectorField nf = boundary[patchi].nf();

            // Reset nHatPatch to correspond to the contact angle

            scalarField a12 = nHatp & nf;

            scalarField b1 = cos(theta);

            scalarField b2(nHatp.size());

            forAll(b2, facei)
            {
                b2[facei] = cos(acos(a12[facei]) - theta[facei]);
            }

            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());
        }
    }
}


void Foam::threePhaseInterfaceProperties::calculateK()
{
    const volScalarField& alpha1 = mixture_.alpha1();

    const fvMesh& mesh = alpha1.mesh();
    const surfaceVectorField& Sf = mesh.Sf();

    // Cell gradient of alpha
    volVectorField gradAlpha = fvc::grad(alpha1);

    // Interpolated face-gradient of alpha
    surfaceVectorField gradAlphaf = fvc::interpolate(gradAlpha);

    // Face unit interface normal
    surfaceVectorField nHatfv = gradAlphaf/(mag(gradAlphaf) + deltaN_);
    correctContactAngle(nHatfv.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_);
    //nHat.boundaryField() = nHatfv.boundaryField();
    //K_ = -fvc::div(nHatf_) + (nHat & fvc::grad(nHatfv) & nHat);
}


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

Foam::threePhaseInterfaceProperties::threePhaseInterfaceProperties
(
    const threePhaseMixture& mixture
)
:
    mixture_(mixture),
    cAlpha_
    (
        readScalar
        (
            mixture.U().mesh().solutionDict().subDict("PISO").lookup("cAlpha")
        )
    ),
    sigma12_(mixture.lookup("sigma12")),
    sigma13_(mixture.lookup("sigma13")),

    deltaN_
    (
        "deltaN",
        1e-8/pow(average(mixture.U().mesh().V()), 1.0/3.0)
    ),

    nHatf_
    (
        (
            fvc::interpolate(fvc::grad(mixture.alpha1()))
           /(mag(fvc::interpolate(fvc::grad(mixture.alpha1()))) + deltaN_)
        ) & mixture.alpha1().mesh().Sf()
    ),

    K_
    (
        IOobject
        (
            "Kcond",
            mixture.alpha1().time().timeName(),
            mixture.alpha1().mesh()
        ),
        -fvc::div(nHatf_)
    )
{
    calculateK();
}


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