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Unsteady Laminar Flow Around a circular cylinder

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Old   December 29, 2007, 11:44
Default Unsteady Laminar Flow Around a circular cylinder
  #1
Mehmet Sonmez
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Hi,

I am investigating the behaviour of liquid water around a circular cylinder. Reynolds number is 178, and the velocity is 0.0008942m/s. But I couldn't get the velocity contour as it should be.

Here is the image of how it should be. http://img186.imagevenue.com/img.php..._122_425lo.JPG

And this is what I got(It is definitely wrong) http://img11.imagevenue.com/img.php?..._122_930lo.JPG

Can anybody help me? I chose unsteady solver and laminar for viscous. Time Step Size, Number of Step Size, Max Iter. per Time Step, have they any impact on the result?
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Old   December 29, 2007, 12:55
Default Re: Unsteady Laminar Flow Around a circular cylind
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Ramesh.K
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Hi, when u are solving unsteady flow time step plays a major role in predicting the physics of the flow. Timestep is calculated based on v=del(x)/del(t) where del t should be ur time step. u can see it in fluent manual how to calculate the time step. if accurate time step is not specified the solution will not be correct.

bye
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Old   December 29, 2007, 15:03
Default Re: Unsteady Laminar Flow Around a circular cylind
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Mehmet Sonmez
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Thank you very much, Ramesh.K
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Old   December 31, 2007, 01:13
Default Re: Unsteady Laminar Flow Around a circular cylind
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Sham
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Ramesh is right that time step is very important. In choosing a time step, try to keep the cell CFL (Courant) number to be below 1 near the cylinder. Also, you have to run it long enough to be able to get some vortex shedding and may be need to introduce some perturbation to stimulate shedding.

Sham.
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Old   January 3, 2008, 06:28
Default Re: Unsteady Laminar Flow Around a circular cylind
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vinse
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hi, How to calculate the number of time step per iterations in an unsteady problem. thanks in advance

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Old   January 3, 2008, 06:33
Default Re: Unsteady Laminar Flow Around a circular cylind
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Sham
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In my opinion thats does not really matter as long as your time step size is small enough. In m simulation, it takes about 5 iterations per time step.
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