hitech
01-03-2003, 07:42 PM
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):
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):