Running a 3d simulation of flow through a blockage, I was trying to calculate, in surface integrals, the mass flow rates through planes at different locations downstream. Expecting to get constant values in the planes I was evaluating, the values seem to vary a fair bit. The flow is fairly complicated but the residuals are quite low, most are below 1e-6 although continuity is nearing 1e-5. In this compressible simulation, the planes that were most obviously incorrect had flow in both directions, recirculation zones. Is this because of the way Fluent evaluates a dot product of the area vector and the velocity vector? Any ideas? Thanks a lot.

How have u defined the bc? with compressible flows u should you a mass flow inlet and not a velocity inlet.

Hi, thanks for your response.

I have defined the inlet and outlet as pressure BC's. In gambit I defined a couple of interior surfaces that give the right mass flow rate but when I create my own planes in Fluent it gives values that are considerable larger. I'm not sure why that is.

Thanks again, -philip