Average velocity within a region
 

Hello, I am new to Paraview.
I am working on a problem in OpenFOAM and now i need to get the average values of vertical velocity within a region for some timesteps in Paraview. It is rising bubble of air inside water. How to get it? I tried used "contour" , then "slice" and "integrate variables" but in the end i think i am confused. Initial position:

https://sun1-23.userapi.com/hNaO3pYg...fxQnJ2lXhM.jpg

Please,help. Thanks a lot.

I am used "contour" and made isosurface for alpha.water = 0.5 , but i dont know how to choose whole area inside this contour and then use for it "integrate variables". Anybody knows? Thanks