[jianglong]

Dear all, Here I have a simple question about the calculation of flow rate. Already, I have calculated the transient flow rates across the patches. How can I cumulate them to a sum value (total mass transport) over time? From my knowledge, Mass is equal to the sum(flux*deltaT). Or it can be calculated by cumulative trapezoidal numerical integration, such as deltaT*(flux1+flux2)/2. Any difference or which could be more suitable? Will these two methods introduce the error of mass balance?

[Tobi]

Hey,

you can use FO to calculate the flux at a patch (or faceZone) and integrate the data over time. This is possible by using the functionObject feature in OpenFOAM. In your case we should be able to do it somehow in that way:

functions
{
    massThroughPatch
    {
        type    surfaceFieldValue;
        libs    (fieldFunctionObjects);

        // Adjust yourself
        writeControl    adjustableRunTime;
        writeInterval   0.1;
        writeFields     false;

        regionType  patch;
        name        <YOURPATCH>;

        log         true;

        operation   integrate;  // << use some non-sense to see the list of operations we can use
        fields
        (
            phi
        );
    }
}