Hi' I am having problems with understanding the boundary conditions for compressible flow.

I have a gas pipe with a gas pressure on 3barg, which enters into many small straigh pipes that is connected to the ambient.

I try to model only the small pipe (one) and the flow into ambient.

I set the operation pressure to 1 bar. I set the the inlet boundary to the small pipe as a pressure inlet, with Gauge Total pressure to 3 barg. The supersonic/initial gauge pressure I have set to zero. (I really do not understand what is meant with the supersonic/initial gauge pressure)

I know the static temperature in the gas pipe, but I assume it is the total temperature I have to set for the inlet.

Any help is appreciated

Hi,

Supersonic/initial gauge pressure has no effect on your boundary condition if your problem is subsonic but when mach number exceeds 1 then this pressure will came into account, also I suggest you to set mass flow at the inlet B.C.

Let me know if you are successful in solving your problem. Sina

In case of compressible flow if problem is subsonic it has been told there is no effect of supersonic or initial gauge pressure. in my case initial pressure is 4 bar. Can i give that supersonic or initial gauge pressure is 2 bar or 0 bar. please suggest