Info<< "Reading field p\n" << endl;
    volScalarField p
    (
        IOobject
        (
            "p",
            runTime.timeName(),
            mesh,
            IOobject::READ_IF_PRESENT,
            IOobject::NO_WRITE
        ),
        mesh,
        dimensionedScalar("0", dimensionSet(0, 2, -2, 0, 0), 1.0)
    );

    Info<< "Reading physical velocity field U" << endl;
    Info<< "Note: only if voidfraction at boundary is 1, U is superficial velocity!!!\n" << endl;
    volVectorField U
    (
        IOobject
        (
            "U",
            runTime.timeName(),
            mesh,
            IOobject::READ_IF_PRESENT,
            IOobject::NO_WRITE
        ),
        mesh,
        dimensionedVector("0", dimensionSet(0, 1, -1, 0, 0), Foam::vector::zero)
    );

//========================
// drag law modelling
//========================


    Info<< "\nReading voidfraction field voidfraction = (Vgas/Vparticle)\n" << endl;
    volScalarField voidfraction
    (
        IOobject
        (
            "voidfraction",
            runTime.timeName(),
            mesh,
            IOobject::READ_IF_PRESENT,
            IOobject::AUTO_WRITE
        ),
        mesh,
        dimensionedScalar("0", dimensionSet(0, 0, 0, 0, 0), 1.)
    );


    Info<< "Reading particle velocity field Us\n" << endl;
    volVectorField Us
    (
        IOobject
        (
            "Us",
            runTime.timeName(),
            mesh,
            IOobject::READ_IF_PRESENT,
            IOobject::AUTO_WRITE
        ),
        mesh,
        dimensionedVector("0", dimensionSet(0, 1, -1, 0, 0), Foam::vector::zero)
    );

//========================
#   include "createPhi.H"

    label pRefCell = 0;
    scalar pRefValue = 0.0;
    setRefCell(p, mesh.solutionDict().subDict("PISO"), pRefCell, pRefValue);


    singlePhaseTransportModel laminarTransport(U, phi);

    autoPtr<incompressible::turbulenceModel> turbulence
    (
        incompressible::turbulenceModel::New(U, phi, laminarTransport)
    );