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Asymmetric solution for bluff bodies symmetric tandem

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Old   March 13, 2014, 14:40
Default Asymmetric solution for bluff bodies symmetric tandem
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Hello,
has anybody experience with an asymmetric average solution for two symmetric bluff bodies in tandem?

What I'm wonder is: is there a specific value for the ratio between the width of the bodies and the gap between them for which no vortex shedding occurs but instead a transverse shear layer is present between the two bodies and this shear layer is actually stable in time?

What I'm guessing is:
If the two bodies are too close to each other they behave like a single body and no vortex shedding occurs between them.
If they are really far away then they behave like two different bodies with vortex shedding after both of them.

Now, what happens in between? Can an asymmetric wake exist? If so, is there any paper on this?

Thanks a lot

Bud
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Old   March 13, 2014, 16:19
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Filippo Maria Denaro
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I don't understand your statement:

a single body and no vortex shedding occurs

as vortex shedding appears always after a critical number is reached
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Old   March 13, 2014, 16:24
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Filippo,
what I meant is that if the gap between the two bodies is too small (compared to the width of them) then you don't get any vortex shedding in the region between the bodies as the vortices don't get to roll, that independently on the Re. Of course you'll get vortex shedding after the second body if Re is high enough.
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Old   March 13, 2014, 16:32
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Quote:
Originally Posted by bud_el_lodituma View Post
Filippo,
what I meant is that if the gap between the two bodies is too small (compared to the width of them) then you don't get any vortex shedding in the region between the bodies as the vortices don't get to roll, that independently on the Re. Of course you'll get vortex shedding after the second body if Re is high enough.
Ok, I see now, but I suppose that in the gap you still have (at high Re) vortical structures that are unsteady even if they are "confined" by the separated flow ...
Many years ago I did some 2D simulations for tandem configuration, you can read

G. de Felice, F.M. Denaro, C. Meola; "Stream-Function Based Multiple Bluff Bodies 2D Flow Analysis"; Journal of Wind Engineering and Industrial Aerodynamics, Vol. 50, pp. 49-61, 1993
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Old   March 13, 2014, 16:39
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Thanks again for your help Filippo.
So, if I understand correctly you don't think it is possible to have an asymmetric vortical transverse structure in the gap between the bodies, right?
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Old   March 13, 2014, 17:21
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well, in a statistical sense I think you can obtain an "averaged steady vortical structure" between the bodies, I doubt the pointwise unsteady field can have such a single structure at high Re ...
I think about the flow structure between the bodies as a sort of lid driven cavity where the stress forcing is provided by the external flow..
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Old   March 18, 2014, 01:22
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Was searching for a different topic, but I believe this paper'll aid this discussion

http://www.sciencedirect.com/science...89974611001927
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Old   March 18, 2014, 16:07
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Thanks Somdeb. I had a quick look, it doesn't seem they experienced any clear asymmetry in the wake but I'll have a deeper look later!
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