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Old   July 20, 2007, 09:58
Default divergence detected
  #1
German Montalvo
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I am working in a compressor stage, I am trying to validate the model with results of other software CFX, so replicated the whole model in terms of the geometry and boundary conditions as well initial conditions, though after a few iterations the simulations stops with the following error message "Error: divergence detected in AMG solver: temperature" I check everything over and over but seems that the problem is not there, though I noticed temperature and pressure limited in the volumes of my model. So I wonder if anyone could help me out on this in order to figure it out.

Thanks in advance.

German
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Old   July 20, 2007, 10:26
Default Re: divergence detected
  #2
Joe
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You cannot setup CFX and Fluent absolutely identically. There are under-the-hood differences.

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Old   July 20, 2007, 10:31
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German Montalvo
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So there are differences beyond my control, because of the code of Fluent?
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Old   July 20, 2007, 10:46
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Joe
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Yup.
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Old   July 20, 2007, 16:18
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AAA
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Hey

Try lowering the under-relaxation Factor for energy to 0.5 as well as density and see if it works.

Regards

AAA
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Old   July 20, 2007, 16:26
Default Re: divergence detected
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red lemon
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Never lower energy to anything less than 0.98. Try disabling secondary temperature gradients, fmg initialisation, pressure based coupled solver with low CFL.
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Old   July 20, 2007, 18:07
Default Re: divergence detected
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AAA
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Hi Again

Red lemon is right. The energy under-relaxation factor must be between 0.95 to 1.0. What I meant was to lower it for a while to see if an initial solution can be reached, then bump it back to 1.0 for the final solution.

Sorry

AAA
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Old   July 23, 2007, 08:35
Default Re: divergence detected
  #8
German Montalvo
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How I disable the secondary temperature gradients?
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Old   July 23, 2007, 18:08
Default Re: divergence detected
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red lemon
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Type this into the window : (rpsetvar 'temperature/secondary-gradient? #f)
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Old   July 24, 2007, 07:49
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  #10
German Montalvo
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Under which menu?, because I typed into the window, but does not recognize the command.
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Old   July 24, 2007, 13:50
Default Re: divergence detected
  #11
red lemon
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Type the entire line including brackets into the Fluent windows and hit return. This will disable them and make the solution more stable.
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