Unbale to get stable transonic flow

Alex

Hello,

a simple transonic flow in a Laval nozzle is under consideration with subsonic pressure inlet and transonic outlet. The trouble is that the density becomes negative and solution blows up.

I have the following setup:

Stagnation Inlet; Pressure Outlet with mean "on"; thermal formulation: total enthalpy, adiabatic walls.

PISO, stationary, ideal gas f(T,P)

URF pressure 0.001, momentum 0.7, pressure correction sweeps 100. URF density 0.9.

I increased the pressure at stagnation inlet in steps so the flow becomes supersonic in the nozzle.

The trouble is on outlet where the shock waves should go outside of the domain. In my opinion transient wawe BC should garantee that. I already tried the transient BC (in an transient calculation) on outlet and the Riemann BC (stationary) but it was not better.

Does anybody has some ideas how to avoid solution instability?