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Can this solution be regarded as converged?

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Old   April 1, 2011, 06:15
Default Can this solution be regarded as converged?
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I am simulating turbulent flow with conjugate heat transfer and I have specified the following convergence criteria:

RMS residual for mass, momentum and energy equations as 1E-6. AND Conservation target as 0.001%

Now I am facing trouble with getting the required convergence. Please refer the attached residual plots. The residual for mass drops below 1e-6. But residual for momentum stabilizes around 1e-5 and that for energy around 5e-6. Regarding the conservation target, the maximum domain imbalance is around 0.006% for H-energy for the fluid domain.

Can this solution be regarded as converged. The question may sound stupid as clearly the specified convergence criteria has not been met. But I had no theoretical basis for specifying 1e-6 as the convergence criteria in the first place. Had i specified 1e-5 as the convergence criteria for equations with no criteria for conservation target, I would not have even observed this behavior.
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File Type: png Momentum_and_mass_residuals.png (14.1 KB, 36 views)
File Type: png Heat_Transfer_residuals.png (10.7 KB, 32 views)
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Old   April 1, 2011, 07:10
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It might a good idea to show the same plots again but when it is solved an a finer mesh, apply a gloabl scaling factor to reduce element size, to see if the convergence changes.
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Old   April 1, 2011, 09:24
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Looks like good convergence to me! Check the T-Energy imbalance in the solid just to be safe, but I expect it's fine.
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Old   April 3, 2011, 06:42
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This question has been asked hundreds of times.... So I wrote an FAQ:

http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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