[ripudaman]

Hi fellow Foamers,

I am having some trouble identifying the best way to calculate the boundaryField average on a patch. I have tried three techniques and all of them give me different answers :-

label wallPatch1 = mesh.boundaryMesh().findPatchID("ff");
scalar area1 = gSum(mesh.magSf().boundaryField()[wallPatch1]);
if (area1 > 0)
{
    sumW111 = gSum
    (
        mesh.magSf().boundaryField()[wallPatch1]
      * mag(D.boundaryField()[wallPatch1])
    ) / area1;
}
forAll(D.boundaryField()[wallPatch1], face1)
{
    D1 = D.boundaryField()[wallPatch1][face1];
    N1 = mesh.Sf().boundaryField()[wallPatch1][face1]
         /mesh.magSf().boundaryField()[wallPatch1][face1];
    disp1 = -1.0 * (D1.component(vector::X) * N1.component(vector::X));
    disp1+= -1.0 * (D1.component(vector::Y) * N1.component(vector::Y));
    disp1+= -1.0 * (D1.component(vector::Z) * N1.component(vector::Z));
    disp1 = disp1/mag(N1);
    sumW1+=mag(disp1);
    sumW11+=mag(D.boundaryField()[wallPatch1][face1]);
    nF1+=1;
}
Info<<sumW1/nF1<<nl<<sumW11/nF1<<nl<<sumW111<<nl;

For the above code different values are printed to the screen. What am I missing here?

FYI, the above snippet is added as a separate .H file in the runTime loop.

Foamers please help me here.

Thank you.
Regards,
Ripu

[jherb]

For OpenFOAM operators see: http://www.foamcfd.org/Nabla/guides/...sGuidese4.html

I guess you want the inner/dot product of the surface vectors of the patch with your field? Then you have to use the operator "&" instead of "*" in your sum for W111. At least for W1 you are calculating the inner product. W11 just sums the unweighted absolute values of your field on the patch to calculate the mean of all these values.

So in fact, you calculate three different thing. They would be equal, if all faces of the patch had the same size and the field was parallel to the faces' normal vectors.

[ripudaman]

Joachim,

Thank you very much for the explanation. I highly appreciate it.

Regards,
Ripu