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Odd residual behaviour for Two Layer K Epsilon

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Old   February 28, 2012, 06:01
Default Odd residual behaviour for Two Layer K Epsilon
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David Van Cauwenberge
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I am currently pursuing my Master's thesis using CFD-ACE to simulate flow inside finned tubes. As results for realizable K-epsilon with two-layer wall function were way off, I'm currently using the standard "Two Layer K Epsilon" turbulence model.

The results are fine but my residuals always follow a similar behaviour:

After normal behaviour for the first 100-500 iterations, the kinetic energy and afterwards the dissipation rate residuals start rising and fluctuating greatly while the others will no longer drop. Anyone have an idea what might be causing this?

Many thanks in advance.
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Old   March 7, 2012, 06:47
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The residuals fluctuate when the flow encounters the fins. Try similar geometry without fins and you wont see the fluctuations. You can tighten the relaxation factors to decrease the fluctuations. The fluctuations are not harmful. They only delay convergence.
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