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

U = dimensionedVector("0", U.dimensions(), vector::zero);

surfaceScalarField phi
(
    IOobject
    (
        "phi",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),
    fvc::interpolate(U) & mesh.Sf()
);

if (args.optionFound("initialiseUBCs"))
{
    U.correctBoundaryConditions();
    phi = fvc::interpolate(U) & mesh.Sf();
}


// Default name for the pressure field
word pName("p");

// Update name of the pressure field from the command-line option
args.optionReadIfPresent("pName", pName);

// Infer the pressure BCs from the velocity BCs
wordList pBCTypes
(
    U.boundaryField().size(),
    fixedValueFvPatchScalarField::typeName
);

forAll(U.boundaryField(), patchi)
{
    if (U.boundaryField()[patchi].fixesValue())
    {
        pBCTypes[patchi] = zeroGradientFvPatchScalarField::typeName;
    }
}

Info<< "Constructing pressure field " << pName << nl << endl;
volScalarField p
(
    IOobject
    (
        pName,
        runTime.timeName(),
        mesh,
        IOobject::READ_IF_PRESENT,
        IOobject::NO_WRITE
    ),
    mesh,
    dimensionedScalar(pName, sqr(dimVelocity), 0),
    pBCTypes
);

Info<< "Constructing velocity potential field Phi\n" << endl;
volScalarField Phi
(
    IOobject
    (
        "Phi",
        runTime.timeName(),
        mesh,
        IOobject::READ_IF_PRESENT,
        IOobject::NO_WRITE
    ),
    mesh,
    dimensionedScalar("Phi", dimLength*dimVelocity, 0),
    p.boundaryField().types()
);

label PhiRefCell = 0;
scalar PhiRefValue = 0;
setRefCell
(
    Phi,
    potentialFlow.dict(),
    PhiRefCell,
    PhiRefValue
);
mesh.setFluxRequired(Phi.name());