Specific mass flow rate in a pipe-like subdomain

James

Hi, I'm a beginner and I have a simple problem:

I need to set an specific value for the mass flow rate at a fluid subdomain limited by a single thin surface.

Or set an specific velocity for a flow that pass trought a surface.

Or something that alows me to fix the flow rate for a pipe at a specific location, not inthe inlet nor the outlet.

Thank you very much

James