I m studying supersonic flow behaviour through nozzles.I m unable to identify the boundary condition at outlet of diverging part of nozzle which always behaves like diffuser instaed of nozzle.

so anyone who can help is welcome.

hi whether at inlet the flow is subsonic or supersonic? if at inlet of nozzle the flow is subsonic then divergent acts as not diffuser, rather it will increase velocity.

Actually,I m using convergent-divergent nozzle to get supersonic conditions at outlet(divergent part)from subsonic inlet conditions at convergent part of nozzle.But i m not able to identify boundary conditions(i m giving pressure inlet & outlet BC)which can yield the result.

hi first of all before the convergent portion, u should give some area of 3 or four times the convergent diameter and then prescribe the pr inlet boundary at that end and at divergent portion u give pr outlet boundary condition. initially while solving u decrease the urf and try to gradually increase it, such that at convergence the urf should come to default. ok