UEqn.H

    MRF.correctBoundaryVelocity(U);

    fvVectorMatrix UEqn
    (
        fvm::ddt(U) + fvm::div(phi, U)
      + MRF.DDt(U)
      + turbulence->divDevReff(U)
     ==
        parcels.SU(U, true)
      + fvOptions(U)
    );

    UEqn.relax();

    fvOptions.constrain(UEqn);

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

        fvOptions.correct(U);
    }