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how to identify transient simulation converged

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Old   January 22, 2009, 07:59
Default how to identify transient simulation converged
  #1
littlelz
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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
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Old   January 22, 2009, 13:27
Default Re: how to identify transient simulation converged
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sa
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when your lift and drag curve reaches to some periodic fluctuations.
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Old   January 22, 2009, 17:26
Default Re: how to identify transient simulation converged
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Glenn Horrocks
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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
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Old   January 27, 2009, 05:26
Default Re: how to identify transient simulation converged
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littlelz
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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
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Old   January 27, 2009, 16:25
Default Re: how to identify transient simulation converged
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Glenn Horrocks
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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
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Old   January 27, 2009, 18:13
Default Re: how to identify transient simulation converged
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anne
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oh, I see.

many thanks for your help. all the best
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