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Help request; how do capture vortex shedding?

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Old   August 27, 2007, 14:19
Default Help request; how do capture vortex shedding?
  #1
sina
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Hi;

I really appreciate if any one could give some hints on my problem. I have a flow over a bluff boddy at Re=3e+5. I did steady simulation with perfect convergence(order of residuals: e-8).

then I continued with unsteady simulation with time step of 0.05s and 1000 time steps and saved data file with frequency of 10. the residuals continued to decrease to e-10.

Now, I am stuck on how to catch time varying propeties of the flow specially vortex shedding as I compare contours of velocity in different autosaved data files and I cant see any difference between them!!!

I'll wait your help. thanks.
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Old   August 27, 2007, 19:53
Default Re: Help request; how do capture vortex shedding?
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Sham
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Sina,

Not sure what you are asking here. If you wnat to observe vortex shedding, go to display>contours and select velocity and by vorticity magnitude. Then unselect auto range and change the range say from 0.0001 to 1. If you successfully get vortex shedding, you should be able to see them.

Sham.
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Old   August 28, 2007, 02:31
Default Re: Help request; how do capture vortex shedding?
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palani kumar
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hi sina.. what is the order of ur velocity..??if it is high - around 100 m/s then the vortex shedding may be faster..it depends on the dimensions of the bluff body too..

unsteady timesteps of 0.05s is a bit large..u can try giving 0.001s for 1000 iterations saving data files at a freq of 10..and u may use the contours of stream functions instead of velocity to check up the vortex..or plot vectors of velocity..

try plotting stream function contours with ur present data and then if u dont notice any considerable change in the flow field reduce ur timestep and then the frequency of writing data files..

hope this one helps..

regards, palani.

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Old   August 28, 2007, 16:52
Default Re: Help request; how do capture vortex shedding?
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Jake
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Are you using a turbulence model? It may be supressing the shedding. Also realize that there is a range of mid-level Reynolds numbers in which there is no shedding.

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Old   August 29, 2007, 19:03
Default Re: Help request; how do capture vortex shedding?
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sina
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thanks all for your help.

I am using RK-e model and as I said the Re number is 3e+5 which is not so low I think.

thanks again and I wait for more comments.
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Old   August 30, 2007, 16:55
Default Re: Help request; how do capture vortex shedding?
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sina
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thanks all for your help.

but can any body say how I can get the shedding frequency?
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