The run diverges sometimes

fatihyaman661 · May 15, 2024, 02:23

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?

colinda1 · May 21, 2024, 10:44

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

May 15, 2024, 02:23	The run diverges sometimes	#1
fatihyaman661 New Member Fatih Yaman Join Date: Sep 2023 Posts: 1 Rep Power: 0	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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May 21, 2024, 10:44		#2
colinda1 Senior Member Colinda Join Date: May 2012 Location: Brussels Posts: 152 Rep Power: 14	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