UEqn.H

    MRF.correctBoundaryVelocity(U);

    fvVectorMatrix UEqn
    (
        fvm::ddt(rho, U) + fvm::div(phi, U)
      + MRF.DDt(rho, U)
      + turbulence->divDevRhoReff(U)
     ==
        fvOptions(rho, U)
    );

    UEqn.relax();

    fvOptions.constrain(UEqn);

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

        fvOptions.correct(U);
        K = 0.5*magSqr(U);
    }