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Old 10-11-2015, 10:59 PM   #13 (permalink)
gone-ot
...beats walking...
 
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Quote:
Originally Posted by freebeard View Post
Replying to myself again. I can't link into the middle of a Youtube video, but at 8m08s in it talks about Boeing's wind tunnel with an array of 100 microphone that listen to the air flowing over the aeroform.

There's a formula for estimating the sound (HZ) waves created by air turbulence over smooth surfaces...works on the nutating (left/right and up/down) wanderings of the air pressures as they are created within the air turbulence. I'd guess that's what the microphones are listening for.

This Wiki illustration shows *how* this sonic (Von Karman vortex) nutation occurs:



from this Wiki page: https://en.wikipedia.org/wiki/K%C3%A..._vortex_street




where "ƒ·d/V" is called the "Strouhal Number" and:

f = vortex shedding frequency
d = diameter of cylinder
V = flow velocity

A published UK workshop presentation: http://wwwf.imperial.ac.uk/ssherw/bb..._Meneghini.pdf

...and a NASA paper: https://info.aiaa.org/tac/ASG/FDTC/D...-1218-1989.pdf

Last edited by gone-ot; 10-11-2015 at 11:47 PM..
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