How to ascertain convergence

hedley · June 7, 2014, 01:24

In laymans terms how would one check if solution is converging or has solved . Any practical example eg look at xxxx column in the history file and if it started at 11.2 in value it should reduce to yy in 5000 iterations .

Stating residuals should be 6 orders of magnitude less just confuses me .

hlk · June 10, 2014, 12:45

Thank you for your question.
The residuals are printed as the log of their value. This means that for a 6 order of magnitude decrease the number printed should decrease by 6. In your example, a six order of magnitude convergence would be indicated by 11.2 - 6 = 5.2. The number of iteration it takes to converge will depend heavily on the problem, the mesh, and the CFD settings chosen. Tools like multigrid and the CFL number can accelerate convergence.

hedley · June 10, 2014, 12:51

Thank you for this - I have been watching the output and 5000 iterations on my PC take approximately 3 hours and the residuals hardly move - This is on the sample wing SU2_CFD turb_RAM6.cfg

has anyone run this on a PC so I know what to expect

June 7, 2014, 01:24	How to ascertain convergence	#1
hedley Member Hedley Join Date: May 2014 Posts: 52 Rep Power: 11	In laymans terms how would one check if solution is converging or has solved . Any practical example eg look at xxxx column in the history file and if it started at 11.2 in value it should reduce to yy in 5000 iterations . Stating residuals should be 6 orders of magnitude less just confuses me .

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June 10, 2014, 12:45		#2
hlk Senior Member Heather Kline Join Date: Jun 2013 Posts: 309 Rep Power: 13	Thank you for your question. The residuals are printed as the log of their value. This means that for a 6 order of magnitude decrease the number printed should decrease by 6. In your example, a six order of magnitude convergence would be indicated by 11.2 - 6 = 5.2. The number of iteration it takes to converge will depend heavily on the problem, the mesh, and the CFD settings chosen. Tools like multigrid and the CFL number can accelerate convergence.

June 10, 2014, 12:51		#3
hedley Member Hedley Join Date: May 2014 Posts: 52 Rep Power: 11	Thank you for this - I have been watching the output and 5000 iterations on my PC take approximately 3 hours and the residuals hardly move - This is on the sample wing SU2_CFD turb_RAM6.cfg has anyone run this on a PC so I know what to expect