BrownianMotionForce.C

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    Copyright (C) 2021 OpenCFD Ltd.
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#include "BrownianMotionForce.H"
#include "mathematicalConstants.H"
#include "fundamentalConstants.H"
#include "demandDrivenData.H"
#include "turbulenceModel.H"

using namespace Foam::constant;

// * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * * //

template<class CloudType>
Foam::tmp<Foam::volScalarField>
Foam::BrownianMotionForce<CloudType>::kModel() const
{
    const objectRegistry& obr = this->owner().mesh();
    const word turbName =
        IOobject::groupName
        (
            turbulenceModel::propertiesName,
            this->owner().U().group()
        );

    const turbulenceModel* turb = obr.findObject<turbulenceModel>(turbName);

    if (turb)
    {
        return turb->k();
    }

    FatalErrorInFunction
        << "Turbulence model not found in mesh database" << nl
        << "Database objects include: " << obr.sortedToc()
        << abort(FatalError);

    return nullptr;
}


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

template<class CloudType>
Foam::BrownianMotionForce<CloudType>::BrownianMotionForce
(
    CloudType& owner,
    const fvMesh& mesh,
    const dictionary& dict
)
:
    ParticleForce<CloudType>(owner, mesh, dict, typeName, true),
    rndGen_(owner.rndGen()),
    lambda_(this->coeffs().getScalar("lambda")),
    kPtr_(nullptr),
    turbulence_(this->coeffs().getBool("turbulence")),
    ownK_(false),
    useSpherical_(this->coeffs().getOrDefault("spherical", true))
{}


template<class CloudType>
Foam::BrownianMotionForce<CloudType>::BrownianMotionForce
(
    const BrownianMotionForce& bmf
)
:
    ParticleForce<CloudType>(bmf),
    rndGen_(bmf.rndGen_),
    lambda_(bmf.lambda_),
    kPtr_(nullptr),
    turbulence_(bmf.turbulence_),
    ownK_(false),
    useSpherical_(bmf.useSpherical_)
{}


// * * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * //

template<class CloudType>
Foam::BrownianMotionForce<CloudType>::~BrownianMotionForce()
{
    if (ownK_)
    {
        deleteDemandDrivenData(kPtr_);
        ownK_ = false;
    }
}


// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //

template<class CloudType>
void Foam::BrownianMotionForce<CloudType>::cacheFields(const bool store)
{
    if (turbulence_)
    {
        if (store)
        {
            tmp<volScalarField> tk = kModel();
            if (tk.movable())
            {
                // Take ownership
                kPtr_ = tk.ptr();
                ownK_ = true;
            }
            else
            {
                kPtr_ = &tk.cref();
                ownK_ = false;
            }
        }
        else
        {
            if (ownK_)
            {
                deleteDemandDrivenData(kPtr_);
                ownK_ = false;
            }
        }
    }
}


template<class CloudType>
Foam::forceSuSp Foam::BrownianMotionForce<CloudType>::calcCoupled
(
    const typename CloudType::parcelType& p,
    const typename CloudType::parcelType::trackingData& td,
    const scalar dt,
    const scalar mass,
    const scalar Re,
    const scalar muc
) const
{
    forceSuSp value(Zero);

    const scalar dp = p.d();
    const scalar Tc = td.Tc();

    const scalar alpha = 2.0*lambda_/dp;
    const scalar cc = 1.0 + alpha*(1.257 + 0.4*exp(-1.1/alpha));

    // Boltzmann constant
    const scalar kb = physicoChemical::k.value();

    scalar f = 0;
    if (turbulence_)
    {
        const label celli = p.cell();
        const volScalarField& k = *kPtr_;
        const scalar kc = k[celli];
        const scalar Dp = kb*Tc*cc/(3*mathematical::pi*muc*dp);
        f = sqrt(2.0*sqr(kc)*sqr(Tc)/(Dp*dt));
    }
    else
    {
        const scalar s0 =
            216*muc*kb*Tc/(sqr(mathematical::pi)*pow5(dp)*sqr(p.rho())*cc);
        f = mass*sqrt(mathematical::pi*s0/dt);
    }

    Random& rnd = this->owner().rndGen();

    if (useSpherical_)
    {
        // To generate a spherical distribution:
        const scalar theta = rnd.sample01<scalar>()*twoPi;
        const scalar u = 2*rnd.sample01<scalar>() - 1;

        const scalar a = sqrt(1 - sqr(u));
        const vector dir(a*cos(theta), a*sin(theta), u);

        value.Su() = f*mag(rnd.GaussNormal<scalar>())*dir;
    }
    else
    {
        // Generate a cubic distribution (3 independent directions)
        value.Su() = f*rnd.GaussNormal<vector>();

        // OLD CODE for cubic distribution
        // const scalar sqrt2 = sqrt(2.0);
        // for (direction dir = 0; dir < vector::nComponents; dir++)
        // {
        //     const scalar x = rnd.sample01<scalar>();
        //     const scalar eta = sqrt2*Math::erfInv(2*x - 1.0);
        //     value.Su()[dir] = f*eta;
        // }
    }

    return value;
}


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