[Sxq]

Hi

I'm new to CFD and trying to understand convergence criteria and residuals

I hear that convergence criteria should be set to ex. 10^-3, 10^-6 and that the solution has converged when it reaches this value. However I find that typically the residuals will start at 0 and then decrease, decreasing more slowly as the number gets smaller, eventually reach a state that is more or less steady.

So what is the point of selecting a convergence value at all? It seems that selecting a convergence value lower than this steady state value will cause the residuals to never reach convergence and simply run until the maximum iterations have been performed. Setting a value higher than this steady state value causes it to converge before actual convergence has been reached.

So clearly I don't understand something properly, and any help would be appreciated.

[Zaktatir]

You have to judge convergence by means of the variations of key variables behaviour in you simulation, the imbalances from the flux report and not only the Residuals. Latter only depict the change of the rate of change of the solution from iteration to iteration

[wyldckat]

Greetings to all!
I was browsing by (while hunting down spammers ) and noticed this thread.

Have a look at this old thread that should explain a lot about the topic of "convergence": http://www.cfd-online.com/Forums/flu...nvergence.html