reversed flow in over-expanded supersonic nozzle
 

hi All,
got a headache with convergence of the solution because of reversed flow.

i do have over-expanded supersonic nozzle where the back-flow presents at the end of the nozzle wall.

pressure inlet- 6 bar (means 5 bar as gauge pressure) + To- 800K
pressure outlet- 1 bar (absolute) + To- 300K
reference- 1 bar

tried first order, solution steering, limits. nothing helps... once I got reversed flow the solution is down..

NB: have no problem with the same nozzle in CFX (using the opening at the outlet). The reason I'd like to use Fluent is because of the CUT-CELL mesh.

Any suggestion or ideas on how to get rid of the reversed flow at the end of the nozzle wall? pls help.