[Ledeniso]

Hello dears,

[aligoger]

There is a curtain way to calculate volume flow rate over the specific patch in ParaView.

1. Take a slice of your wall by using filter slice
2. Apply a integrateVariables in filter
3 Apply the calculator in Filter. Change your attribute mode in cell data in calculator filter than calculate your average Uz by U_Z/Volume
3.Change your attribute mode in cell data integrateVariables window.
4. You will see there your avarage Uz value and area of your specified wall.
5. Open another calculator and use Uzaverage*Area. Do not forget to work in cell data mode
6. Finally, you will see your flow rate in your integrateVariables window.

OR

You need to write program in OpenFoam.

I hope it helps.