foam-extend4.1-coherent-io/applications/solvers/compressible/steadyCompressibleFoam/UEqn.H

    // Solve the momentum equation
    U.storePrevIter();

    fvVectorMatrix UEqn
    (
        fvm::ddt(rho, U)
      + fvm::div(phi, U)
      + turbulence->divDevRhoReff(U)
    );

    UEqn.relax();

    solve(UEqn == -fvc::grad(p));