[immortality]

where the below codes for limiting velocity on a patch should be added in rhoPimpleFoam?

word patchName = "NAME_OF_THE_PATCH";
label patchID = mesh.boundary().findPatchID(patchName2);

  forAll(U.boundaryField()[patchID],faceI)
  {
     U.boundaryField()[patchID][faceI].component(0)=some value;
  }

rhoPimpleFoam.C is this:

#include "fvCFD.H"
#include "basicPsiThermo.H"
#include "turbulenceModel.H"
#include "bound.H"
#include "pimpleControl.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

int main(int argc, char *argv[])
{
    #include "setRootCase.H"
    #include "createTime.H"
    #include "createMesh.H"

    pimpleControl pimple(mesh);

    #include "createFields.H"
    #include "initContinuityErrs.H"

    // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

    Info<< "\nStarting time loop\n" << endl;

    while (runTime.run())
    {
        #include "readTimeControls.H"
        #include "compressibleCourantNo.H"
        #include "setDeltaT.H"

        runTime++;

        Info<< "Time = " << runTime.timeName() << nl << endl;

        #include "rhoEqn.H"

        // --- Pressure-velocity PIMPLE corrector loop
        while (pimple.loop())
        {
            #include "UEqn.H"
            #include "hEqn.H"

            // --- Pressure corrector loop
            while (pimple.correct())
            {
                #include "pEqn.H"
            }

            if (pimple.turbCorr())
            {
                turbulence->correct();
            }
        }

        runTime.write();

        Info<< "ExecutionTime = " << runTime.elapsedCpuTime() << " s"
            << "  ClockTime = " << runTime.elapsedClockTime() << " s"
            << nl << endl;
    }

    Info<< "End\n" << endl;

    return 0;
}

where UEqn.H is:

// Solve the Momentum equation

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

UEqn().relax();

volScalarField rAU(1.0/UEqn().A());

if (pimple.momentumPredictor())
{
    solve(UEqn() == -fvc::grad(p));
    K = 0.5*magSqr(U);
}

hEqn.H:

{
    fvScalarMatrix hEqn
    (
        fvm::ddt(rho, h)
      + fvm::div(phi, h)
      - fvm::laplacian(turbulence->alphaEff(), h)
     ==
        dpdt
      - (fvc::ddt(rho, K) + fvc::div(phi, K))
    );

    hEqn.relax();
    hEqn.solve();

    thermo.correct();
}

pEqn.H:

rho = thermo.rho();
rho = max(rho, rhoMin);
rho = min(rho, rhoMax);
rho.relax();

U = rAU*UEqn().H();

if (pimple.nCorrPISO() <= 1)
{
    UEqn.clear();
}

if (pimple.transonic())
{
    surfaceScalarField phid
    (
        "phid",
        fvc::interpolate(psi)
       *(
            (fvc::interpolate(U) & mesh.Sf())
          + fvc::ddtPhiCorr(rAU, rho, U, phi)
        )
    );

    while (pimple.correctNonOrthogonal())
    {
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvm::div(phid, p)
          - fvm::laplacian(rho*rAU, p)
        );

        pEqn.solve(mesh.solver(p.select(pimple.finalInnerIter())));

        if (pimple.finalNonOrthogonalIter())
        {
            phi == pEqn.flux();
        }
    }
}
else
{
    phi =
        fvc::interpolate(rho)*
        (
            (fvc::interpolate(U) & mesh.Sf())
          + fvc::ddtPhiCorr(rAU, rho, U, phi)
        );

    while (pimple.correctNonOrthogonal())
    {
        // Pressure corrector
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvc::div(phi)
          - fvm::laplacian(rho*rAU, p)
        );

        pEqn.solve(mesh.solver(p.select(pimple.finalInnerIter())));

        if (pimple.finalNonOrthogonalIter())
        {
            phi += pEqn.flux();
        }
    }
}

#include "rhoEqn.H"
#include "compressibleContinuityErrs.H"

// Explicitly relax pressure for momentum corrector
p.relax();

// Recalculate density from the relaxed pressure
rho = thermo.rho();
rho = max(rho, rhoMin);
rho = min(rho, rhoMax);
rho.relax();
Info<< "rho max/min : " << max(rho).value()
    << " " << min(rho).value() << endl;

U -= rAU*fvc::grad(p);
U.correctBoundaryConditions();
K = 0.5*magSqr(U);

dpdt = fvc::ddt(p);