FreeStream.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 "FreeStream.H"
#include "constants.H"
#include "tetIndices.H"
 
using namespace Foam::constant::mathematical;
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
template<class CloudType>
Foam::FreeStream<CloudType>::FreeStream
(
    const dictionary& dict,
    CloudType& cloud
)
:
    InflowBoundaryModel<CloudType>(dict, cloud, typeName),
    patches_(),
    moleculeTypeIds_(),
    numberDensities_(),
    particleFluxAccumulators_()
{
    // Identify which patches to use
 
    DynamicList<label> patches;
 
    forAll(cloud.mesh().boundaryMesh(), p)
    {
        const polyPatch& patch = cloud.mesh().boundaryMesh()[p];
 
        if (isType<polyPatch>(patch))
        {
            patches.append(p);
        }
    }
 
    patches_.transfer(patches);
 
    const dictionary& numberDensitiesDict
    (
        this->coeffDict().subDict("numberDensities")
    );
 
    List<word> molecules(numberDensitiesDict.toc());
 
    // Initialise the particleFluxAccumulators_
    particleFluxAccumulators_.setSize(patches_.size());
 
    forAll(patches_, p)
    {
        const polyPatch& patch = cloud.mesh().boundaryMesh()[patches_[p]];
 
        particleFluxAccumulators_[p] = List<Field<scalar>>
        (
            molecules.size(),
            Field<scalar>(patch.size(), Zero)
        );
    }
 
    moleculeTypeIds_.setSize(molecules.size());
 
    numberDensities_.setSize(molecules.size());
 
    forAll(molecules, i)
    {
        numberDensities_[i] = numberDensitiesDict.get<scalar>(molecules[i]);
 
        moleculeTypeIds_[i] = cloud.typeIdList().find(molecules[i]);
 
        if (moleculeTypeIds_[i] == -1)
        {
            FatalErrorInFunction
                << "typeId " << molecules[i] << "not defined in cloud." << nl
                << abort(FatalError);
        }
    }
 
    numberDensities_ /= cloud.nParticle();
}
 
 
 
// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
 
template<class CloudType>
Foam::FreeStream<CloudType>::~FreeStream()
{}
 
 
// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
template<class CloudType>
void Foam::FreeStream<CloudType>::autoMap(const mapPolyMesh& mapper)
{
    CloudType& cloud(this->owner());
    const polyMesh& mesh(cloud.mesh());
 
    forAll(patches_, p)
    {
        label patchi = patches_[p];
 
        const polyPatch& patch = mesh.boundaryMesh()[patchi];
        List<Field<scalar>>& pFA = particleFluxAccumulators_[p];
 
        forAll(pFA, facei)
        {
            pFA[facei].setSize(patch.size(), 0);
        }
    }
}
 
 
template<class CloudType>
void Foam::FreeStream<CloudType>::inflow()
{
    CloudType& cloud(this->owner());
 
    const polyMesh& mesh(cloud.mesh());
 
    const scalar deltaT = mesh.time().deltaTValue();
 
    Random& rndGen = cloud.rndGen();
 
    scalar sqrtPi = sqrt(pi);
 
    label particlesInserted = 0;
 
    const volScalarField::Boundary& boundaryT
    (
        cloud.boundaryT().boundaryField()
    );
 
    const volVectorField::Boundary& boundaryU
    (
        cloud.boundaryU().boundaryField()
    );
 
 
    forAll(patches_, p)
    {
        label patchi = patches_[p];
 
        const polyPatch& patch = mesh.boundaryMesh()[patchi];
 
        // Add mass to the accumulators.  negative face area dotted with the
        // velocity to point flux into the domain.
 
        // Take a reference to the particleFluxAccumulator for this patch
        List<Field<scalar>>& pFA = particleFluxAccumulators_[p];
 
        forAll(pFA, i)
        {
            label typeId = moleculeTypeIds_[i];
 
            scalar mass = cloud.constProps(typeId).mass();
 
            if (min(boundaryT[patchi]) < SMALL)
            {
                FatalErrorInFunction
                    << "Zero boundary temperature detected, check boundaryT "
                    << "condition." << nl
                    << nl << abort(FatalError);
            }
 
            scalarField mostProbableSpeed
            (
                cloud.maxwellianMostProbableSpeed
                (
                    boundaryT[patchi],
                    mass
                )
            );
 
            // Dotting boundary velocity with the face unit normal
            // (which points out of the domain, so it must be
            // negated), dividing by the most probable speed to form
            // molecularSpeedRatio * cosTheta
 
            scalarField sCosTheta
            (
                (boundaryU[patchi] & -patch.faceAreas()/mag(patch.faceAreas()))
              / mostProbableSpeed
            );
 
            // From Bird eqn 4.22
 
            pFA[i] +=
                mag(patch.faceAreas())*numberDensities_[i]*deltaT
               *mostProbableSpeed
               *(
                   exp(-sqr(sCosTheta)) + sqrtPi*sCosTheta*(1 + erf(sCosTheta))
                )
               /(2.0*sqrtPi);
        }
 
        forAll(patch, pFI)
        {
            // Loop over all faces as the outer loop to avoid calculating
            // geometrical properties multiple times.
 
            const face& f = patch[pFI];
 
            label globalFaceIndex = pFI + patch.start();
 
            label celli = mesh.faceOwner()[globalFaceIndex];
 
            const vector fC = patch.faceCentres()[pFI];
 
            scalar fA = mag(patch.faceAreas()[pFI]);
 
            List<tetIndices> faceTets = polyMeshTetDecomposition::faceTetIndices
            (
                mesh,
                globalFaceIndex,
                celli
            );
 
            // Cumulative triangle area fractions
            List<scalar> cTriAFracs(faceTets.size(), Zero);
 
            scalar previousCummulativeSum = 0.0;
 
            forAll(faceTets, triI)
            {
                const tetIndices& faceTetIs = faceTets[triI];
 
                cTriAFracs[triI] =
                    faceTetIs.faceTri(mesh).mag()/fA
                  + previousCummulativeSum;
 
                previousCummulativeSum = cTriAFracs[triI];
            }
 
            // Force the last area fraction value to 1.0 to avoid any
            // rounding/non-flat face errors giving a value < 1.0
            cTriAFracs.last() = 1.0;
 
            // Normal unit vector *negative* so normal is pointing into the
            // domain
            const vector n = -normalised(patch.faceAreas()[pFI]);
 
            // Wall tangential unit vector. Use the direction between the
            // face centre and the first vertex in the list
            const vector t1 = normalised(fC - (mesh.points()[f[0]]));
 
            // Other tangential unit vector.  Rescaling in case face is not
            // flat and n and t1 aren't perfectly orthogonal
            const vector t2 = normalised(n ^ t1);
 
            scalar faceTemperature = boundaryT[patchi][pFI];
 
            const vector& faceVelocity = boundaryU[patchi][pFI];
 
            forAll(pFA, i)
            {
                scalar& faceAccumulator = pFA[i][pFI];
 
                // Number of whole particles to insert
                label nI = max(label(faceAccumulator), 0);
 
                // Add another particle with a probability proportional to the
                // remainder of taking the integer part of faceAccumulator
                if ((faceAccumulator - nI) > rndGen.sample01<scalar>())
                {
                    nI++;
                }
 
                faceAccumulator -= nI;
 
                label typeId = moleculeTypeIds_[i];
 
                scalar mass = cloud.constProps(typeId).mass();
 
                for (label i = 0; i < nI; i++)
                {
                    // Choose a triangle to insert on, based on their relative
                    // area
 
                    scalar triSelection = rndGen.sample01<scalar>();
 
                    // Selected triangle
                    label selectedTriI = -1;
 
                    forAll(cTriAFracs, triI)
                    {
                        selectedTriI = triI;
 
                        if (cTriAFracs[triI] >= triSelection)
                        {
                            break;
                        }
                    }
 
                    // Randomly distribute the points on the triangle.
 
                    const tetIndices& faceTetIs = faceTets[selectedTriI];
 
                    point p = faceTetIs.faceTri(mesh).randomPoint(rndGen);
 
                    // Velocity generation
 
                    scalar mostProbableSpeed
                    (
                        cloud.maxwellianMostProbableSpeed
                        (
                            faceTemperature,
                            mass
                        )
                    );
 
                    scalar sCosTheta = (faceVelocity & n)/mostProbableSpeed;
 
                    // Coefficients required for Bird eqn 12.5
                    scalar uNormProbCoeffA =
                        sCosTheta + sqrt(sqr(sCosTheta) + 2.0);
 
                    scalar uNormProbCoeffB =
                        0.5*
                        (
                            1.0
                          + sCosTheta*(sCosTheta - sqrt(sqr(sCosTheta) + 2.0))
                        );
 
                    // Equivalent to the QA value in Bird's DSMC3.FOR
                    scalar randomScaling = 3.0;
 
                    if (sCosTheta < -3)
                    {
                        randomScaling = mag(sCosTheta) + 1;
                    }
 
                    scalar P = -1;
 
                    // Normalised candidates for the normal direction velocity
                    // component
                    scalar uNormal;
                    scalar uNormalThermal;
 
                    // Select a velocity using Bird eqn 12.5
                    do
                    {
                        uNormalThermal =
                            randomScaling*(2.0*rndGen.sample01<scalar>() - 1);
 
                        uNormal = uNormalThermal + sCosTheta;
 
                        if (uNormal < 0.0)
                        {
                            P = -1;
                        }
                        else
                        {
                            P = 2.0*uNormal/uNormProbCoeffA
                               *exp(uNormProbCoeffB - sqr(uNormalThermal));
                        }
 
                    } while (P < rndGen.sample01<scalar>());
 
                    vector U =
                        sqrt(physicoChemical::k.value()*faceTemperature/mass)
                       *(
                            rndGen.GaussNormal<scalar>()*t1
                          + rndGen.GaussNormal<scalar>()*t2
                        )
                      + (t1 & faceVelocity)*t1
                      + (t2 & faceVelocity)*t2
                      + mostProbableSpeed*uNormal*n;
 
                    scalar Ei = cloud.equipartitionInternalEnergy
                    (
                        faceTemperature,
                        cloud.constProps(typeId).internalDegreesOfFreedom()
                    );
 
                    cloud.addNewParcel(p, celli, U, Ei, typeId);
 
                    particlesInserted++;
                }
            }
        }
    }
 
    Info<< "    Particles inserted              = "
        << returnReduce(particlesInserted, sumOp<label>()) << endl;
 
}
 
 
// ************************************************************************* //