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Old   March 6, 2007, 17:50
Default vortex shedding
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Altug Basol
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Hallo,

I am trying to solve a 2D flow around a rectangle in cartesian domain. I am using stream function vorticity formulation finite difference formulation. I have applied no-slip boundary conditions on the rectangle. My problem is I could not have vortex shedding when I increase the Re number. In my case the size of the vortexes at the back of the rectangle grow as I increase the Re number but shedding does not appear. Can I solve this problem if I increase the number of grids around the rectangle. I would be thankful if anybody can make me any suggestions.

Thank you very much

Altug
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Old   March 6, 2007, 19:01
Default Re: vortex shedding
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Harish
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Usually you need to introduce some sort of disturbance to speed up the vortex shedding or else it takes a long time.Another possible reason might be as you said not enough points in the boundary layer.Use a stretching function if you want to reduce mesh size near cylinder surface and not increase the number of points.
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Old   March 7, 2007, 06:17
Default Re: vortex shedding
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Al
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try to apply a small disturbance on the grid, for example the upper contour of the rectangle, to break the symmetry of the problem. Alberto
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Old   March 7, 2007, 07:02
Default Re: vortex shedding
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TITAN Algorithms
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http://www.titanalgorithms.com/works...der_sqr_fe.JPG

http://www.titanalgorithms.com/works...esh_coarse.JPG

http://www.titanalgorithms.com/works..._mesh_fine.JPG

http://www.titanalgorithms.com/works...transducer.JPG

Observe the second and third figures. In this simulation, which sounds to be very similar to yours, the coarse mesh does not produce the vortex street (second figure), while the refined mesh, same geometry and Reynolds number, will result in a vortex street. Links available at:

www.TITANAlgorithms.com/workspace_cfd

Kind Regards,

www.TITANAlgorithms.com

Last edited by wyldckat; March 9, 2014 at 17:16. Reason: removed direct images that were showing publicity, as the site is now dead
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Old   March 7, 2007, 18:47
Default Re: vortex shedding
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Altug Basol
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Thank you (Al, Harish and TITAN Algorithms) very much for your attention and suggestions.

Altug

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Old   March 9, 2007, 16:39
Default Re: vortex shedding
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Mani
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It surprises me that no one has pointed this out, but it's probably because we assume you know this already: Vortex shedding is an unsteady phenomenon. You don't mention solving the unsteady equations, nor did you say anything about the temporal resolution you are using. Temporal resolution (small time steps) is just as important as spatial resolution (small grid cells). Coarseness in both space and time will have the effect of suppressing the instability of the steady flow, and hence suppressing vortex shedding.
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