Odd residual behaviour for Two Layer K Epsilon

dvcauwe · February 28, 2012, 06:01

Hello,

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.

cdf_user · March 7, 2012, 06:47

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.

February 28, 2012, 06:01	Odd residual behaviour for Two Layer K Epsilon	#1
dvcauwe New Member David Van Cauwenberge Join Date: Feb 2012 Location: Ghent, Belgium Posts: 19 Rep Power: 14	Hello, 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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March 7, 2012, 06:47		#2
cdf_user Member Join Date: Mar 2011 Posts: 50 Rep Power: 15	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.