Outlet Boundary Conditions

benbru

In college I took a class on CFD. It was enough to make me really interested in CFD, but not enough to become an expert.

Anyways my prof said that you should basically always use a pressure boundary instead of an outlet. Her reason was that with a pressure wall the flow can recirculate back into the fluid domain where as with an outlet it can't. If the fluid really would recirculate in this area then you should not constrain it not to (in fact I hear it can make your solution diverge).

I was wondering if anybody had another opinion on this. I designed an air intake duct for an engine and using the pressure boundary the flow did indeed show some recirc. I think in reality this would not happen because the intake would probally pull in the air before it can recirculate.

Maybe I need to use a pressure boundary with vacuum pressure instead of atmospheric pressure?