shifting from Unsteady to steady

Abhinav

Hi, I am grad student in univ of michigan. I was trying to simulate supersonic flow through a convergent-divergent nozzle. I have two questions. Firstly, I am suppose to get shock waves at outlet of nozzle as final solution as my model mach no is more than 3.5. I am getting it also but as I simulate more, shock waves disappears but max. velocity at outlet remains same. I am using unsteady solver and k epsilon standard model. Can anyone tell me y shock waves are disappearing and also y simulation results are not stabilizing.

Secondly, I am trying to shift from unsteady to steady solver after I get good shock waves but solution is getting divergence. For unsteady state I am using time step of 1e-8. My grid is fine enough for my simulation ( 1e-12 grid area ).

Please give me some suggestions. Thanks in Advance.