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-   -   steady to unsteady (http://www.cfd-online.com/Forums/fluent/82307-steady-unsteady.html)

wlt_1985 November 23, 2010 03:48

steady to unsteady
 
how to implement the results obtained from steady state modeling to unsteady state modeling? is it just switch the steady state condition to unsteady state condition in solver after the steady state condition has been converged?

Thanks

KristianEtienne November 23, 2010 04:46

Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

wlt_1985 November 23, 2010 06:34

Quote:

Originally Posted by KristianEtienne (Post 284441)
Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

Thanks for help. :)

wlt_1985 November 24, 2010 03:10

Quote:

Originally Posted by KristianEtienne (Post 284441)
Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

should i reinitialize before unsteady state modeling?

KristianEtienne November 24, 2010 04:06

No, why would you want to do that? :)

That will reset your solution to what it was before you started the steady simulation..

wlt_1985 November 24, 2010 04:43

Quote:

Originally Posted by KristianEtienne (Post 284563)
No, why would you want to do that? :)

That will reset your solution to what it was before you started the steady simulation..

Thanks for help

Ozgur_ December 4, 2010 17:17

Hey everyone,

I wanted to ask a couple of stuff related to unsteady modelling: I'm doing the exact same thing you discussed; I first get a converged steady-state solution, then I run it unsteady. Here's what happens though:

- I'm analyzing the wake of a 3D cylinder in cross flow. Since for most Re numbers (including mine) the wake is unsteady, so the contour plots of variables oscillate inside the wake.
The funny thing is, for the first 90 - 100 time steps, the wake oscillates, but after that point, and even when the residuals go down and flatten out at low levels, the wake oscillation disappears. The wake looks symmetric, like the average, mean version of all the oscillations.

Any idea why this is happening? Could it be related to the size of the time step and/or the number of pseudo-time iterations at each time step? Or could it be related to the boundary conditions?

Cheers,

Ozgur


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