problem well placed from the point of view of the bc

[WalterCFD]

dear colleagues (very more experienced and prepared than me...),
I have a problem with boundary conditions... more than a problem with a dilemma. .
I have a subsonic air flow and constant density that enters and exits from a pipe, which has as unique peculiarity the asymmetry between inlet and outlet.
while incoming I am quiet with the mass_flow_inlet, outgoing I tried to impose both the outflow and the pressure_outlet:
the first gives me a clean result while the second takes a nice reversed flow on the exit. .
But if I'm not mistaken, the mass_flow_inlet/outflow coupling should lead to a bad problem from the point of view of the bc...

What is your opinion? Do you know texts dealing with this subject?

Thank you.

walter

 

[Vmax]

the outflow condition is a very weak condition on circulation flows, I would not recommend using it unless there are particular reasons.
pressure_outlet condition is better to formulate a well-placed problem.
if you have outgoing recirculations is quite serious: even if there are alternatives in terms of boundary conditions, the best thing is to extend the downstream domain a bit to not bring back flow from an exit.
the best texts you can see are the fluent guides.