Divergence in amg solver while using second order scheme

raj · November 2, 2012, 12:51

Hi all
Iam doing a transient combustion analysis with partially premixed model and compressible case. I am using k-e realisable turbulence model. While running the case with all methods set to first order i got good convergence of results. However when i changed to second order schemes i get the amg solver divergence . Kindly suggest me what could be the problem

vicarious · November 2, 2012, 13:34

Second order Schemes got less relaxation to the high gradients because the adjacent cells involved are more( j+2,J-2), thus the high gradients of parameters could result in a bad behavior. Try to decrease your RFs and check the Green-Gause node based in solver panel.

Regards.

raj · November 2, 2012, 23:39

Hi Thanks for the reply
I have reduced the relaxation factors and the solver is running. But i would like to ask one thing whether by reducinf the RF's does it alter the final results?

cfd seeker · November 3, 2012, 01:10

Quote:

Originally Posted by raj

Hi Thanks for the reply
I have reduced the relaxation factors and the solver is running. But i would like to ask one thing whether by reducinf the RF's does it alter the final results?

No your final solution will remain unaltered however your convergence time will be more with the reduced values of RF's

November 2, 2012, 12:51	Divergence in amg solver while using second order scheme	#1
raj New Member rajkumar Join Date: Oct 2012 Posts: 3 Rep Power: 13	Hi all Iam doing a transient combustion analysis with partially premixed model and compressible case. I am using k-e realisable turbulence model. While running the case with all methods set to first order i got good convergence of results. However when i changed to second order schemes i get the amg solver divergence . Kindly suggest me what could be the problem

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November 2, 2012, 13:34		#2
vicarious Member Pedram Mojtabavi Join Date: Apr 2011 Location: Iran Posts: 66 Rep Power: 15	Second order Schemes got less relaxation to the high gradients because the adjacent cells involved are more( j+2,J-2), thus the high gradients of parameters could result in a bad behavior. Try to decrease your RFs and check the Green-Gause node based in solver panel. Regards.

November 2, 2012, 23:39		#3
raj New Member rajkumar Join Date: Oct 2012 Posts: 3 Rep Power: 13	Hi Thanks for the reply I have reduced the relaxation factors and the solver is running. But i would like to ask one thing whether by reducinf the RF's does it alter the final results?