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von Karman vortex street. Vortices formation mechanism.

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Old   February 17, 2010, 21:00
Default von Karman vortex street. Vortices formation mechanism.
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Hello,
I am not a physicist, but got very interested in von Karman vortex street effect. And I have a question about this effect. I have been googling for an answer for three days but I can't find anything.

It is known for the steady flow around a smooth circular cylinder that:
  • for Re < 5 no separation of the flow occurs;
  • for 5 < Re < 40 a fixed pair of symmetric vortices exists in the flow;
  • for 40 < Re < 200 laminar vortex street exists in the flow.

My question is why the flow changes its regime? I. e. why the vortices appears for Re > 5 and why the vortices begin to shed (and what force makes them to do so) for Re > 40 and what force made them stay (not shed) for Re < 40? Why do they shed in that ("chess-board", "lamp-post", etc) particular order?

Can anyone please explain or point me to such an explanation? And do physicists know how the vortices formation mechanism works at all (I mean may be it is unsolved physics problem)?

Thank you!

P. S. I know the forum is dedicated to CFD. The reason I'm asking here because there are (surprise!) a lot of specialists in fluent dynamics at this forum.
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Old   February 24, 2010, 18:53
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The reason for the change in the structures was discovered by Von Karman and he gave a clear explanation of the reason for the change. Check the book on aeroelasticity by Fung or Batchelor's fluid dynamics.
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