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Interpolation of a volVectorField onto processor patches

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Old   December 22, 2014, 12:43
Default Interpolation of a volVectorField onto processor patches
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Adrien
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Dear all,

I need to compute fluxes over cell faces given a volVectorField. To fulfill the needs of my custom parallel code, the resulting surfaceScalarField requires consistent values across processor patches.

I would like to use a piece of code like this one:

Code:
 phi_ = fvc::interpolate(U_) & mesh_.Sf();
However, I'm running into problems since fvc::interpolate(U) does not yield consistent values on processor patches.

Hence my question: is there any direct way to interpolate a field from cell centers to face centers, with consistent values on processor patches?

To show the inconsistency that I mention, I attached a test case with a Cartesian mesh that has two grid cells and is decomposed onto two processors (i.e., one grid cell per processor). A velocity field U has value (0, 0, 0) on processor 0 and (1, 0, 0) on processor 1. As a result of fvc::interpolate(U), I would expected a value of (0.5, 0, 0) on the processor patch on both processors. However, the (stripped) output is as follows:
Code:
[1] phi = dimensions      [0 1 -2 0 0 0 0];
[1] 
[1] internalField   nonuniform 0();
[1] 
[1] boundaryField
[1] {
[1]     domainBoundary
[1]     {
[1]         type            calculated;
[1]         value           uniform (0 0 0);
[1]     }
[1]     procBoundary1to0
[1]     {
[1]         type            processor;
[1]         value           uniform (0.5 0 0);
[1]     }
[1] }
[0] phi = dimensions      [0 1 -2 0 0 0 0];
[0] 
[0] internalField   nonuniform 0();
[0] 
[0] boundaryField
[0] {
[0]     domainBoundary
[0]     {
[0]         type            calculated;
[0]         value           uniform (0 0 0);
[0]     }
[0]     procBoundary0to1
[0]     {
[0]         type            processor;
[0]         value           uniform (0 0 0);
[0]     }
The values on the patches procBoundary0to1 and procBoundary1to0 are not consistent. Please see the source file testProcessorPatchInterpolation.C for details. The test case can be compiled and run using
Code:
wmake
./Allrun
To circumvent this, I came up with a quick-and-dirty solution which is not satisfactory:

Code:
void
Foam::synchronizeProcessorPatchField
(
    volVectorField& vf
)
{
    const polyBoundaryMesh& patches = vf.mesh().boundaryMesh();

    FieldField<fvPatchField, vector> oldBoundaryField = vf.boundaryField();

    forAll(patches, patchI)
    {
        vf.boundaryField()[patchI].initEvaluate(Pstream::blocking);
    }
    
    forAll(patches, patchI)
    {
        const polyPatch& pp = patches[patchI];
        fvPatchField<vector>& pf = vf.boundaryField()[patchI];
        // The following call puts the values of the patch neighbour field
        // info pf.
        pf.evaluate(Pstream::blocking);

        if (isA<processorPolyPatch>(pp))
        {
            pf = 0.5*(pf.patchNeighbourField() + oldBoundaryField[patchI]);
        }
    }
}
This code is certainly a messy version of a feature which is present somewhere in the OpenFOAM source code. The use of 0.5 as a weighting factor is quite dirty, since it assumes linear interpolation on a Cartesian equidistant grid...

Any input is welcome!

Thanks,
Adrien
Attached Files
File Type: gz testInterpolation.tar.gz (3.4 KB, 7 views)
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Last edited by Mithrandirrr; December 22, 2014 at 12:56. Reason: Missing attached file
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