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 Q January 8, 2006 10:07

I want to know when I perform unsteady cacluation using fluent. Let us suppose I use fixed time stepping method.

And I use certain delta_t=x1 and maximum number of iteration 20 and I also use maximum number of iteration 10 and 4. What is the difference I will get in the results.

How can I optimze delta_t and maximum number of iteration?

Thanks

Q

 galary January 8, 2006 21:00

In my opinion, maximum number of iteration is number of equation iteration solutionin in one time step.Usually you should choose number of iteration to satisfy convergence and get a stable solution in the time step.In face unsteady case in one time step is regarded as steady case.

 Muhammad Shakaib January 9, 2006 03:36

Generally if your time step is correct than there is convergence before 30 iterations this means the residuals drop to atleast an order of magnitude and if you have placed a monitoring point for any variable it becomes stable for last few iterations. The no. of iterations '10' appears to be enough for small time step (than needed) but 4 iterations does not seem suitable.

 Q January 9, 2006 04:48

Hello I am running a unsteady case I would like to know what kind of message I would be getting during this iterations whether I will get message that the solution is converged in 10 iterations if suppose I am using the maximum number of ietartions to be 30.

Q

 Muhammad Shakaib January 9, 2006 08:50

While iterating if the residuals drop below the values (of residuals) that you have set message will be ' solution is converged' and next time step will be started.

 Q January 9, 2006 12:24

what is the typical value of residuals you set?

 Muhammad Shakaib January 14, 2006 00:08

 Muhammad Shakaib January 14, 2006 00:11

Sorry for prevoius empty reply. I just clicked the'post message' due to mistake. I keep my residuals for continiuty 1e-5 for others 1e-3. But these values depends on the case so this may not help you.

Thanks

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