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-   -   Convergence Problem Supersonic Flow Laval Nozzle (https://www.cfd-online.com/Forums/cfx/21903-convergence-problem-supersonic-flow-laval-nozzle.html)

 Tobias December 5, 2005 11:55

Convergence Problem Supersonic Flow Laval Nozzle

Hello I simulate a Laval Nozzle. The nozzle is part of a real wind channel and the part which creates supersonic flow at the outlet (Ma >2.0). I use subsonic pressure inlet (total pressure, total temperature) and supersonic outlet. Two Problems occur, maybe somebody got some advices (solution strategies) for me:

First, overall massflow is too small (no shock occurs!!)

If I choose massflow inlet, solution crashs because of to big mach number.

Thanks to you, Tobias.

 Bart Prast December 6, 2005 07:21

Re: Convergence Problem Supersonic Flow Laval Nozz

1. Use the expert parameter: max continuity loops = 2 (you should always do this for supersonic flows) 2. Do not start up with a supersonic outlet as it will not be a supersonic outlet when you start the calculation. Start first with a pressure boundary untill you have supersonic conditions at the outlet (then switch over)

 Bart Prast December 6, 2005 07:24

Re: Convergence Problem Supersonic Flow Laval Nozz

I forgot:

How can you use a supersonic outlet condition when you expect a shock????? The flow will be subsonic after the shock and at the exit of your nozzle.

 tobias December 7, 2005 02:23

Re: Convergence Problem Supersonic Flow Laval Nozz

Thanks for your advices Bart, I'll try them. I studied the modelling guide and suggest now the same way how to solve this porblem.

By definition of a supersonic outlet I supposed CFX to find the solution without the present of a shock, but I failed. If it works, I'll report.

Thaks to you, tobias.

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