openfoam/applications/solvers/multiphase/bubbleFoam/createPhia.H

    IOobject phiaHeader
    (
        "phia",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ
    );


    surfaceScalarField* phiaPtr;

    if (phiaHeader.headerOk())
    {
        Info<< "Reading face flux field phia\n" << endl;

        phiaPtr = new surfaceScalarField
        (
            IOobject
            (
                "phia",
                runTime.timeName(),
                mesh,
                IOobject::MUST_READ,
                IOobject::AUTO_WRITE
            ),
            mesh
        );
    }
    else
    {
        Info<< "Calculating face flux field phia\n" << endl;

        wordList phiTypes
        (
            Ua.boundaryField().size(),
            calculatedFvPatchScalarField::typeName
        );

        for (label i=0; i<Ua.boundaryField().size(); i++)
        {
            if (isA<fixedValueFvPatchVectorField>(Ua.boundaryField()[i]))
            {
                phiTypes[i] = fixedValueFvPatchScalarField::typeName;
            }
        }

        phiaPtr = new surfaceScalarField
        (
            IOobject
            (
                "phia",
                runTime.timeName(),
                mesh,
                IOobject::NO_READ,
                IOobject::AUTO_WRITE
            ),
            fvc::interpolate(Ua) & mesh.Sf(),
            phiTypes
        );
    }

    surfaceScalarField& phia = *phiaPtr;