Flow over terrain instability of OF by pressure profiles
 

Dear all,
I have more or less a generic question hope to find someone who has experience with that.
I simulate flow over a terrain, it works for incompressible as well as for compressible in steadystate and transient ( here I use (simple -and pimpleFoam, rhosimple- and rhopimpleFoam respectively).
My U-inlet is a U-Profile (vs height). I set total pressure (single value) at the other side for pressure BC outlet.
However if I try use a pressure profile (vs height) then it always crases. Currently I’am not able to run rhosimpleFoam successfully, after 3s, I got the error Message FOAM FATAL ERROR: [1] Negative initial temperature T0: -234.778. (Of course I read a lot of threads about this error messages without solution.)
No matter what I put on the other sides on the BC and I also played around with fv solution fv sceme entries as well as with fine and coarse meshes. It doesn't work at all. I have the feeling that the more I specify (in the BC) the more problems I got (e.g if I put pressure profiles at al 4 Boundary sides or when I try to use also temperature profiles as BC…) .
I heard that OF becomes instable in general if I specify pressure profiles at the BC. Can someone confirm this?