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Strouhal number for sphere and high Re

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Old   October 13, 2016, 05:56
Default Strouhal number for sphere and high Re
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Dear members and experts,
I need to roughly approximate the strouhal-number for a sphere in free flow.
The free velocity of surrounding air is 10-45 m/s, e.g. a high Re above 1e6

The literature and works I've found mainly treats much lower Re

Looking for St number for cylinders does not seem to be appropriate, since I believe the number should be considerably higher for a sphere in this Re region.

What is a good approximation of St in this region?

Any help is much appreciated

best regards,
Fred
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Old   October 18, 2016, 12:34
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Hi, I'm not very knowledgeable about this, but I thought there is an upper critical Reynolds number of about ~3e5 for vortex shedding of spheres no? Could be wrong but what if you don't have large scale oscillations at all? I'm sure you can find plenty on it..
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Old   October 19, 2016, 18:18
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Thanks for the reply!

Yes, you are 100% correct. However, there seems to be a re-establishment of the turbulent vortex street when Re get higher than 3.5e6 (for cylinders) according to lectures and some researchers. see for example slide 5 in the link below (they refer to J. Lienhard):

web.mit.edu/13.42/VIV_2004.ppt

However, I cant find any result concerning spheres. In this case low frequencies were unwanted, so I used a cylinder worst case approximation with St=0.2 and got low, but acceptable frequencies.

I would be interesting to know if the re-establishment only is valid for cylinders.
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Old   October 20, 2016, 08:41
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yeah I recall these coherent structures around cylinders, don't know if something like that exists for spheres and after a 5 minute google I agree that there is not so much work at Re>10e6..
I have the impression there are no observations of that phenomenon though. I found info that beyond 3.7e5 the estabished vortex pair is steady. And a report that shows peaks in the spectrum at up to 1.2e6 attributes this to a vibration in their frame

maybe you can find more! Good luck
Would be interesting to know..
M.
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