Hi all,
In the movingwall example, it uses FluidPressureOutlet3D as its outlet boundary condition.
Is there anyone who knows what the condition exactly is?
Is it pressure condition?

Any opinion would be appreciate!
Thanks a lot.


Hello Maggie,

Yes, the FluidPressureOutlet3D is a “pressure condition”. It copies the unknown populations on the boundary and sets a contant pressure (rho = 1). It is the recommended outflow BC especially for high-Reynolds number flows.


Dear Dimitris,

I’ve been looking on the web, but I could not find any scientific work on the concept behind the FluidPressureOutlet.

Do you know any papers on this?

Thank you,


It’s rather a numerical kitchen trick. There is no paper on the topic AFAIK.

Alright, I see. Thank you.