code_saturne User's Forum

Dear CS team,
I work on a case with multiple outlets and one inlet. The flux is known only at the inlet and it is negative (extraction = the flux is outgoing the domain). The goal is to determine the repartition of ingoing fluxes through the outlets (which outlet/which flux).
These outlets are supposed to be just openings to the ambiant air (P=Patmo).
I used "isolib" BC for my outlets, but I'm not sure they all have a Dirichlet condition on pressure (P=Patmo) since I've read in the user's guide that "The pressure is set to P0 at the first isolib face met. The pressure calibration is always done on a single face, even if there are several outlets."

Can you tell me more on the isolib and Pressure Dirichlet condition when the problem has multiple outlets?
Thanks in advance for your feedback.

Best regards.

Hello,

I'd prefer for others more familiar with the BC details to answer this, but It seems to me (checking the source) that free outlet (isolib) actually use homogeneous Neuman BC's, and P0 is chosen simply based on the fact that in incompressible formulation, only the pressure gradient is used, not the absolute pressure, so that pressure may be chose arbitrarily). if your outlets are all at ambient air, this housl be OK. Otherwise, when using outlets at different pressures, the "ifrent" (free inlet/outlet) BC type may be a better fix, as a head loss may be associated to each outlet.

Best regards,

Yvan

Thank you Yvan for your quick answer.

Regards.