[bieshuxuhe]

hi !
In openfoam-2.2.0 interDyMFoam solver , there is a piece of code that

    while (runTime.run())
    {
        #include "readControls.H"
        #include "alphaCourantNo.H"
        #include "CourantNo.H"

        #include "setDeltaT.H"

        runTime++;

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

        scalar timeBeforeMeshUpdate = runTime.elapsedCpuTime();

        {
            // Calculate the relative velocity used to map the relative flux phi
            volVectorField Urel("Urel", U);

            if (mesh.moving())
            {
                Urel -= fvc::reconstruct(fvc::meshPhi(U));
            }

            // Do any mesh changes
            mesh.update();
        }

        if (mesh.changing())
        {
            Info<< "Execution time for mesh.update() = "
                << runTime.elapsedCpuTime() - timeBeforeMeshUpdate
                << " s" << endl;

            gh = g & mesh.C();
            ghf = g & mesh.Cf();
        }

        if (mesh.changing() && correctPhi)
        {
            #include "correctPhi.H"
        }

        if (mesh.changing() && checkMeshCourantNo)
        {
            #include "meshCourantNo.H"
        }

        twoPhaseProperties.correct();

        #include "alphaEqnSubCycle.H"
        interface.correct();

        // --- Pressure-velocity PIMPLE corrector loop
        while (pimple.loop())

......

The red part code create a Urel , and it means "Calculate the relative velocity used to map the relative flux phi" . But the Urel does not appear again after the code "Urel -= fvc::reconstruct(fvc::meshPhi(U));" ! It is even not written or used , so the relative velocity Urel looks no use in this solver ! If we comment out the red part code , the solver will work well too . (I have tried.)
I am a little confused . I wonder where is Urel used to map the relative flux phi ? executing mapFields ? or we must use it ourselves by adding some lines of code in the solver ?
could you help me ?