I try to model the air flow through a nozzle, can anyone tell me what is the best way to setup the flow domain and what boundary conditions to use, if i only know the up and down stream pressure and the the throat is choked.

if the throat is choked then the downstream conditions dont matter (as they will be supersonic, in the case of a diverging section after the throat) unless you have a normal shock in the nozzle past the throat.

Set up the simulation using the coupled explicit solver, and do an inviscid calculation to start with. Pressure based inlets, or far field boundary as inlet. Pressure as outlet (will be ignored if the outflow is supersonic).

cheers nandu

thank you for your reply, it is very helpful!! i wonder if u can help me with another problem? i want to find the highest exit pressure of the diverging section, while the throat is still choked, and the flow down stream is subsonic.

many thanks!!

this would mean that there is a shock wave in the the diverginging section of the nozzle just downstream of the nozzle throat. the explanation of how this can be calculated can be found in any decent gas dynamics text book. it is an iterative process to match the pressures across a normal shock with supersonic upstrem conditions.

cheers nandu