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-   -   HELP TIME STEP!! (http://www.cfd-online.com/Forums/fluent/33282-help-time-step.html)

merry March 21, 2004 16:30

HELP TIME STEP!!
 
Hello

I am computing an unsteady flow around an obstacle in fluent 6.1. First, I made computations with the steady case. And then when the solution converged I turn on the unsteady case.

I calculated the time step ( time step = T/100= 1.e-3 s) from the strouhal number that gives the shedding frequency (f= 1/T)of the vortex.

The problem, when I started the computations with this time step the solution converged after the 1st iteration. So, I increased the time step (1.e-2) but still the solution is converging after the 1st iteration. and then I increased the time step again and again and again.... every time the solution is converging after the 1st iteration. So, I really don't know what fluent is doing ???? it seems that for any time step the solution is converging.

Can someone explain what is really happening???

thanks

Merry

Zhihua March 25, 2004 14:35

Re: HELP TIME STEP!!
 
I think you can change the convergence criteria in Fluent. It is located at Solve-Monitor. Set a much lower value for convergence of any equations.

merry March 25, 2004 15:38

Re: HELP TIME STEP!!
 
thanks a lot for your suggestion. I'll try that!


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