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The run diverges sometimes

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Old   May 15, 2024, 02:23
Exclamation The run diverges sometimes
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Fatih Yaman
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I am doing a compressor analysis using NUMECA for a company. The work is confidential so I cannot share much detail. The funny thing is that the very same analysis converges sometimes and diverges at other times. But I don't change anything at all. The mesh, the test setup, the model, the boundary conditions are all the same. I just hit run button twice. And the result changes in two.




I use k-w wilcox model and SST model, and both of them show this behaviour. The problem doesn't persist with SA model. I run the analysis multicore on an HPC system that runs on SLURM.




When it diverges; firstly, the residuals act like the way when they converge. They decrease gradually. However, after a point it gives the density negative error and the analysis stops.




What I don't understand is not that the analysis diverges. It is the fact that it converges sometimes and diverges sometimes. Does anyone have any idea why such an indeterministic behaviour may occur?
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Old   May 21, 2024, 10:44
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Colinda
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Hi,
Did you already create a support case on support.cadence.com? For such industrial consultancy project I would recommend to do that to make sure to get an expert advice soon.

When you write about "the residuals", do you also look a the residuals for the turbulence quantities? Di you save the solution before divergence and have a look at it to see whether there are any non-physical values for pressure and temperature in the domain?

Best regards,
Colinda
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