foam-extend4.1-coherent-io/applications/solvers/multiphase/cavitatingFoam/UEqn.H

    surfaceScalarField muEff
    (
        "muEff",
        twoPhaseProperties.muf()
      + fvc::interpolate(rho*turbulence->nut())
    );

    fvVectorMatrix UEqn
    (
        fvm::ddt(rho, U)
      + fvm::div(phi, U)
      - fvm::laplacian(muEff, U)
    //- (fvc::grad(U) & fvc::grad(muf))
      - fvc::div(muEff*(fvc::interpolate(dev(fvc::grad(U))) & mesh.Sf()))
    );

    UEqn.relax();

    if (pimple.momentumPredictor())
    {
        solve(UEqn == -fvc::grad(p));
    }

    Info<< "max(U) " << max(mag(U)).value() << endl;