[Gerry Kan]

Howdy Foamers:

After digging around for the last few days, I still have some questions on how the mapped boundary condition works ...

I am doing an LES simulation in an open channel geometry (wall on the bottom boundary, zeroGradient on the top boundary). I am thinking of taking turbulent sample from the outlet boundary and feed it back to the inlet, where I prescribe some kind of mean velocity / mass flow rate.

It seems that "mappedFlowRate" should do the job, based on the reference in this post (How to properly use mappedFlowRate.

To test the setup I have a rectangular pipe (DX = DY = 1, DZ = 2) with corresponding inlet and outlet.

Here is the relevant parts of my ./system/blockMeshDict:

    inletMap    {
        type            mappedPatch;
        sampleMode      nearestPatchFace;
        samplePatch     outletMap;
        sampleRegion    region0;
        offsetMode      uniform;
        offset          ( 1 0 0 );
        faces           ( (0 4 7 3) );
    }

    outletMap    {
        type            patch;
        faces ( (2 6 5 1) );
    }

and ./0/U

    inletMap    {
        type     mappedFlowRate;
        phi      phi;
        rho      rho;
        neigPhi  phi;
        value    uniform ( 10 0 0 );
    }

    outletMap    {
        type  inletOutlet;
        inletValue  uniform ( 0 0 0 );
        outletValue  uniform ( 0 0 0 );
    }

However, I end up getting effectively a zero flowfield, and without the fluctuations. If I set the inlet- and outlet-Value's in the outletMap to a non-zero vector, e.g., (1 0 0), the solver will crash immediately.

It is very likely I have a false understanding of what the mapped family boundary conditions actually does. I don't know what else is missing.

Gerry.