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CFX High speed wall function-ERROR

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Old   August 23, 2016, 05:33
Default CFX High speed wall function-ERROR
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Fabio
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I'm performing a parallel run with CFX of a supersonic flow inside a tank, using the RNG-K-epsilon turbolent model with the activation of the high- speed Wall Heat Transfer Model..

It's my first time facing with this fluid dynamic problems so I would like to have a discussion about this.

This is the output of ANSYS:

Parallel run: Received message from slave
-----------------------------------------
Slave partition : 3
Slave routine : get_TWFTFC
Master location : End of Continuity Loop
Message label : 009100015
Message follows below - :
+--------------------------------------------------------------------+
| ****** Notice ****** |
| The non-dimensional near wall temperature (T+) has been clipped |
| for calculation of Wall Heat Transfer Coefficient. |
| |
| Boundary Condition : Walls |
| T+ clip value = 1.0000E-10 |
| |
| If this situation persists and you are using the High Speed Model, |
| consider enabling Mach number based blending between low speed and |
| high speed wall functions. You can do so by specifying a Mach |
| number threshold as follows: |
| |
| EXPERT PARAMETERS: |
| highspeed wf mach threshold = 0.1 # default=0.0 (off) |
| END


What should I do in this case? Modify the wall function mach threshould as suggested by the programme, using the text command line?

Thanks for your comprehension!
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Old   August 23, 2016, 06:05
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Glenn Horrocks
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It is more likely that your simulation has resulting in a non-physical solution and is possibly diverging. I would check the result you have to see if something weird is happening. Do not change the mach threshold until you are absolutely sure that your model is correct and that you need to do it.
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Old   August 23, 2016, 06:26
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Quote:
Originally Posted by ghorrocks View Post
It is more likely that your simulation has resulting in a non-physical solution and is possibly diverging. I would check the result you have to see if something weird is happening. Do not change the mach threshold until you are absolutely sure that your model is correct and that you need to do it.
Thank you for your fast response.

The same model starting from 100 Pa as initial pressure works well. Instead, tuning the initial pressure to 5 Pa, the software gives me that error.

I should check if the continuity regime is still valid, shoudn't it?

Regards
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Old   August 23, 2016, 06:50
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Yes, you should check that.

If you save a backup file in the iteration before it crashes you should be able to see where the simulation is going weird. It would be even better if you add the residuals to the results file because then you can see where the residuals are worst, which is likely to be the location of the problem.
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