Problems at transonic flow
 

I simulate compressible flow through a total pressure tube at different Mach numbers. Ma=0,26...0,55 worked fine but I encounter problems at Ma=0,8. As I rise the mass flow at the inlet boundary (to hopefully reach Ma=0,8) there is a jump from Ma=0,59 to Ma=0,88 or higher. I cannot fine-tune the mass-flow to reach Ma=0,8. I use mass-flow-inlet and pressure-outlet BC. Solver settings are segregated, implicit, steady state with std.-k-eps-turbulence model and viscous heating turned on.

Any suggestions what might be wrong when trying to reach transonic flow?