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Convergence Problem Supersonic Flow Laval Nozzle

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Old   December 5, 2005, 11:55
Default Convergence Problem Supersonic Flow Laval Nozzle
  #1
Tobias
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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.
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Old   December 6, 2005, 07:21
Default Re: Convergence Problem Supersonic Flow Laval Nozz
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Bart Prast
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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)
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Old   December 6, 2005, 07:24
Default Re: Convergence Problem Supersonic Flow Laval Nozz
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Bart Prast
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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.
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Old   December 7, 2005, 02:23
Default Re: Convergence Problem Supersonic Flow Laval Nozz
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tobias
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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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