//===============================
// particle interaction modelling
//===============================

Info<< "\nReading momentum exchange field Ksl\n" << endl;
volScalarField Ksl
(
    IOobject
    (
        "Ksl",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
        ),
    mesh
    //dimensionedScalar("0", dimensionSet(1, -3, -1, 0, 0), 1.0)
);

Info<< "\nReading voidfraction field voidfraction = (Vgas/Vparticle)\n" << endl;
volScalarField voidfraction
(
    IOobject
    (
        "voidfraction",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
        ),
    mesh
);
voidfraction.oldTime();

Info<< "Reading particle velocity field Us\n" << endl;
volVectorField Us
(
    IOobject
    (
        "Us",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
        ),
    mesh
);

Info<< "Reading field p_rgh\n" << endl;
volScalarField p_rgh
(
    IOobject
    (
        "p_rgh",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
    ),
    mesh
);

Info<< "Reading field U\n" << endl;
volVectorField U
(
    IOobject
    (
        "U",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
    ),
    mesh
);

Info<< "Reading/calculating face flux field phi\n" << endl;
surfaceScalarField phi
(
    IOobject
    (
        "phi",
        runTime.timeName(),
         mesh,
        IOobject::READ_IF_PRESENT,
        IOobject::AUTO_WRITE
    ),
    linearInterpolate(U*voidfraction) & mesh.Sf()
);

multiphaseMixture mixture(U, phi, voidfraction);

// Need to store rho for ddt(rho, U)
volScalarField rho
(
    IOobject
    (
        "rho",
        runTime.timeName(),
        mesh,
        IOobject::READ_IF_PRESENT,
        IOobject::AUTO_WRITE
    ),
    mixture.rho()
);
rho.oldTime();

volScalarField rhoEps ("rhoEps", rho * voidfraction);

// Construct incompressible turbulence model
autoPtr<incompressible::turbulenceModel> turbulence
(
    incompressible::turbulenceModel::New(U, phi, mixture)
);


#include "readGravitationalAcceleration.H"
#include "readhRef.H"
#include "gh.H"


volScalarField p
(
    IOobject
    (
        "p",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),
    p_rgh + rho*gh
);

label pRefCell = 0;
scalar pRefValue = 0.0;
setRefCell
(
    p,
    p_rgh,
    pimple.dict(),
    pRefCell,
    pRefValue
);

if (p_rgh.needReference())
{
    p += dimensionedScalar
    (
        "p",
        p.dimensions(),
        pRefValue - getRefCellValue(p, pRefCell)
    );
}

mesh.setFluxRequired(p_rgh.name());