Inlet velocity according to the velocity at some interface
 

I am using star ccm to simulate the flow around the building and the resulting airflow rate through an opening in the same building. I have divided my domain into two regions. One the outer atmosphere and the other is inside of the building.

I want to simulate for several opening sizes (i.e. several simulation with different opening sizes) but i also want to keep the same volume flow rate through the opening in each case. (e.g. I want to make sure that the (average) volume flow rate through the opening is 1.5 m3/s in each case).

The opening in the building is also the interface between atmospheric region and inside region. Can anyone help me (or give me an idea) how can I define my inlet velocity (i.e. inlet of atmospheric region) that make sure the surface average velocity in the opening of building is 1m/s.

Ahsan Iqbal
Denmark