Hello.
This is indeed a standard problem. Custom postprocessors like CFD Post has built-in calculating functions to get mass flow averages, integrals etc. ParaView, to my knowledge, doesn’t have this function so you can only do it manually. First and simplest way is to create a target surface like just slice or something curvilinear + thresholds to limit it’s bounds, then use Surface Normals and Calculator filters in series to compute rw=Density*(Velocity.Normals), then integrate with Integrate variables. It will only formally compute the sum of FaceArea*Variable, but inspecting the table for your rw variable column you will find the mass flow through the slice.
Although this method is simple, it’s not convenient because you must create this additional pipeline and then search the table for rw variable (datasets in CFD modeling has lots of variables so if you selected them all you will have a very long table header in Integrate Variables result). Also you will only get the mass flow. To calculate mass flow or area averages you will need to add more filters. Even if you use the custom filter, as I know, it’s not editable so you cannot just add new averaging functions (may be custom filters are editable in newer ParaView versions, sorry, I don’t know).
If you need intensive averaging for many variants and you want to get result as fast as possible and be able to add new functionality relatively easily, you can make a script. I attach my simple script, but you need to customize it for your variables. To use the script, select the target surface (like slice) in pipeline, then run the script from Python console. This is made for ParaView 5.2 (newer versions doesn’t support our “semi-hardware” RDP).
ParaViewSurfaceIntegrals.py (3.6 KB)