Vortex shedding or the von Karman Vortex Street

[hitech]

I probably shouldn't be reposting this, but I'm afraid it is lost in the "spin" thread.

The mysterious "X" force that causes the poor accuracy of a sphere shaped projectile (paintball in our case) appears to be the von Karman Vortex Street phenomenon. This phenomenon causes an oscillating turbulent wake behind a cylinder (or sphere). An oscillating wake would most certainly cause a knuckle ball effect. This appears to be a well-known phenomenon, at least among fluid dynamics guys. Here are a couple of links that demonstrate this phenomenon:

http://www.csa.ru/~ignatiev/examples_2d_1.html
http://kuwahara.isas.ac.jp/KARMAN/KR1.HTM

Another example of this phenomenon is the vibration of a taut wire as air flows past it. If/when the oscillation frequency of the wake matches the resonant frequency of the wire (the frequency the wire vibrates at) the wire vibrates. We have all seen (heard) this before.

It appears that no one is sure what exactly causes this phenomenon. Here are some theories:

http://www.pcnet.com/~jdutka/thesis/thesis1.html

And lastly, a good picture that demonstrates the phenomenon (R = reynolds number):

[bjjb99]

I like the images you provided that show the vortices in effect. Here's a link to a more global version of the same thing (hope the link works, cut-n-paste if necessary):

http://edcw2ks15.cr.usgs.gov:8090/imagegallery/silverstream/pages/pgImageDetail.html?ImageID=151

BJJB


Hmmm... guess it would have helped if I had read the Paintball Spin thread first... same image is shown there. *blush*

[ph0b]

Hitech, can you merge this back with the other thread? I think it'll be better to store pertinent information in one thread (rather than trying to classic this one too).

Thanks!

[Rust]

totaly off topic, but i kind of want to mill or laser engrave that into one of my markers. (also great info, but hey, who's here to actaully learn anything?)