# how to identify transient simulation converged

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 January 22, 2009, 07:59 how to identify transient simulation converged #1 littlelz Guest   Posts: n/a I am just wondering how to know that my transition simulation has converged. actually, I am running a steady state simulation on airfoil case, and I found local convergence problem which, I guess, is caused by seperation bubble moving, i.e. it is actually a transient problem. So I start running transient simulation. what 's your comments on my case, and how do I know it is already converged (I have no experience on transient simulation). tnanks, anyway littlelz

 January 22, 2009, 13:27 Re: how to identify transient simulation converged #2 sa Guest   Posts: n/a when your lift and drag curve reaches to some periodic fluctuations.

 January 22, 2009, 17:26 Re: how to identify transient simulation converged #3 Glenn Horrocks Guest   Posts: n/a Hi, Assuming lift and drag are your key outputs, do a sensitivity check of mesh size, convergence tolerance and time step size (if transient) to assess the level of accuracy of your answer. Glenn Horrocks

 January 27, 2009, 05:26 Re: how to identify transient simulation converged #4 littlelz Guest   Posts: n/a Thanks for your reply. That's what I am concerning; the timestep size in transient simulation. In my case, as I set the time step size very small, say 1e-8, it is converged quickly, 3-5 coeff loops. as I increase it, say 5e-7, it is very slow to reach convergence. What's that mean? how do I decide a proper tiemsetp size? Please advice

 January 27, 2009, 16:25 Re: how to identify transient simulation converged #5 Glenn Horrocks Guest   Posts: n/a Hi, You find the correct timestep size by a sensitivity study. If you are getting 3-5 coeff loops at a timestep of 1e-8 then that is a good place to start as that is about the point where the transient solver usually works best - but check with a sensitivity analysis. Glenn Horrocks

 January 27, 2009, 18:13 Re: how to identify transient simulation converged #6 anne Guest   Posts: n/a oh, I see. many thanks for your help. all the best