How to simulate a fan inside a domain
 

Hello every body.

I have two pipe within my geometry. The airflow was supplied over the inlet 1 and extracted out by outlet 1.
There is a fan in the inner pipe which suck the flow in the inner pipe from outlet 2 and extracted to the main pipe from outlet 2. the flow can pass also from the gap between the shell of inner/outer pipes. How can I specify the boundary condition of inlet/outlet 2? Note that we have no any flow properties at the inlet/outlet 2 except velocity.
I think it is possible to do it with fan-zone, but I cannot find any example for it.
I am appropriate if someone can give me a hand in the case.

Thanks.

Use fan condition and specify pressure jump. Be careful in selecting sign for pressure jump.

I did it already. the problem is the flow is pass throw the walls which I specify to the boundaries around the fan zone. I want flow just passing throw the inlet, outlet of the fan zone, not the walls.
do you have any solution for this issue?