[t.oliveira]

Originally Posted by t.oliveira

I need to compute the integral of U over a plane defined by its basePoint and normalVector. Could you please shed some light on how to do it?

Use the following function object:

functions
{
    flux
    {
        type            faceSource;
        functionObjectLibs ("libfieldFunctionObjects.so");

        enabled         true;
        outputControl   outputTime;
        surfaceFormat   off;

        // Output to log&file (true) or to file only
        log             true;
        // Output field values as well
        valueOutput     true;
        // Type of source: patch/faceZone/sampledSurface
        source          sampledSurface;        
        //// if sampledSurface: dictionary with a sampledSurface
        //// Note: will not sample surface fields.
        sampledSurfaceDict
        {           
            type            plane;
            basePoint       (8.1e-4 0 0);
            normalVector    (1 0 0);
            interpolate       false;
        }
        operation       areaNormalIntegrate;
        fields
        (
            U
        );
    }
}

I saved it in a file called system/integrateOnSurfaceDict, instead of writing it on the bottom of controlDict, just to keep it more organised.

Use it executing:

execFlowFunctionObjects -dict system/integrateOnSurfaceDict -noFlow

To find out this solution, I started looking some examples on /src/postProcessing/functionObjects. It is a good starting point.

I tried also using cuttingPlane instead of plane, and interpolate true, and got slightly different results. If I put the plane over a patch, the usage of plane and interpolate false gave the same result as running

patchIntegrate U <patchName>

Best wishes,

Thomas