Fluid Mechanics in Paintball

[ShooterJM]

Hey guys I've been plotting trajectories and impact velocities of paintballs. Bluntly, I'm not so hot at remembering anything in Fluid Mechanics. So help me out here.

Can I make the assumption that:

A) The Magnus Effect on a smooth sphere will not produce the reverse Magnus Effect anamoly with any regularity whatsoever. Explanation: I don't have a flatline and have never seen one used. Occasionally do the balls drop down instead of a flat trajectory?

B) Air pressure does not have a great dampening effect on the RPM's of a spinning paintball mid-flight. Assume no wind, rain, etc.

Thanks.

[ShooterJM]

Re: Fluid Mechanics in Paintball

Originally posted by ShooterJM

Can I make the assumption that:

A) The Magnus Effect on a smooth sphere will not produce the reverse Magnus Effect anamoly with any regularity whatsoever.

B) Air pressure does not have a great dampening effect on the RPM's of a spinning paintball mid-flight. Assume no wind, rain, etc.

Thanks.

Um. Guess I'll just go ahead and make the assumption

[soilent green]

be patient deep blue doesn't see as much action as the others sorry if this reply wasn't deep blue appropriat just encouraging this guy but as for B. I think the ball from a flatline slows down (its RPM) gradually through its flight

[ShooterJM]

Originally posted by soilent green
be patient deep blue doesn't see as much action as the others sorry if this reply wasn't deep blue appropriat just encouraging this guy but as for B. I think the ball from a flatline slows down (its RPM) gradually through its flight

Yeah, I've noticed that. Actually, I was rather surprised that they let me post, let alone start a new thread. I was kind of expecting to see it deleted or moved quickly. As for the RPM's changing, I think you're correct, but I don't think it's enough to make changes to my program/equations. Thanks!

[AGD]

Shooter, please explain the Magnus effect in detail.

thanks

AGD

[vf-xx]

Paraphrased from the 4th ed Fluid Mechanics textbook byt Frank M. White:

"The magnus effect is negative lift which is proportional to stream velocity and vortex strength. From the streamline patter (I wish I had a scanner) we can tell that the velocity on the top of the cylinder/ball is less and therefore the pressure is higher from Bernoulli's equation; this explains the force. This uses the inviscid theory."

I"m just quoting, we haven't gotten this far in the class yet. Hope it helps.

[ShooterJM]

Originally posted by AGD
Shooter, please explain the Magnus effect in detail.

thanks

AGD

Well there are two main theories on what causes it. As I'm not the greatest about explaining things, here's a passage that I ruthlessly stole from various Advanced Fluid Mechanics textbooks and reworded to be a bit more concise.

Magnus force results from the asymmetric difference of the boundary layer displacement thickness caused by the combined spinning and flow past the sphere. Actually a sphere can impart a spinning motion to only a very thin layer next to the surface. The motion imparted to this layer affects the manner in which the flow separates from the surface in the rear. Boundary layer separation is delayed on the side of the spinning object that is moving in the same direction as the free stream flow, while the separation occurs prematurely on the side moving against the free stream flow. The wake then shifts toward the side moving against the free stream flow. As a result, flow past the object is deflected, and the resulting change in momentum flux causes a force in the opposite direction
This phenomenon is influenced by the conditions in the thin layer next to the body, known as the boundary layer, and there may arise certain anomalies in the force if the spin of the body introduces anomalies in the layer, such as making the flow turbulent on one side and not the other. One such is the reverse Magnus effect which may occur for smooth spheres. (Rough balls such as cricket balls, baseballs, golf balls and tennis balls, do not show this effect. )

In summary, the magnus effect explains why backspin can cause upward lift force on a moving sphere. It's just that when a smooth sphere is used the opposite can sometimes occur (the balls take a dive).

I figured that since the flatline barrel system imparted backspin (and the Z-body as well) perhaps someone would know how often this occurs.

[ShooterJM]

Originally posted by vf-xx
Paraphrased from the 4th ed Fluid Mechanics textbook byt Frank M. White:

"The magnus effect is negative lift which is proportional to stream velocity and vortex strength. From the streamline patter (I wish I had a scanner) we can tell that the velocity on the top of the cylinder/ball is less and therefore the pressure is higher from Bernoulli's equation; this explains the force. This uses the inviscid theory."

I"m just quoting, we haven't gotten this far in the class yet. Hope it helps.

Yeah that's it! I think that assumes the sphere is spinning towards the flow pattern though. Depending the direction of the spin, the delayed boundry layer seperation would change location.

Good luck in the class, it's really fun! Tough, but fun!

[Croix71]

/boggle

reading this post made my head spin...

[ShooterJM]

Originally posted by Croix71
/boggle

reading this post made my head spin...

Sorry. Guess it doesn't really matter. I just want to be able to factor in every little thing into my calculations.

[Croix71]

It's all good. We had an interesting conversation about the whole subject of sphere's and Bernoulli's equation.

We came up with this question.

Would it be possible to have a paintball exit the barrel with a backward rotation (i.e. like you hit a tennis ball with 'slice') so as to have a longer flatter parabolic trajectory?

The opposite of this would be having the paintball exit the barrel with a forward rotation (i.e. like if a tennis ball is hit with a 'top spin'). I think the result would be a steeper parabolic trajectory.

A lot would depend on how fast the the paintball is rotating.

[ShooterJM]

Originally posted by Croix71
It's all good. We had an interesting conversation about the whole subject of sphere's and Bernoulli's equation.

Yeah, It's quite interesting. I'm tempted to go out and buy a Z body just so I can run some tests on it. From those I've spoken to the question of whether backspin can be put on a paintball is moot. It can be done. This is not to say that I've witnessed it at all, just reports from users of the flatline and Z-body. It's the whole smooth sphere anomaly that gets me. I can't figure out how to calculate the frequency of it's occurence.

I guess another angle to take would be to try to figure out exactly at what point a smooth sphere is considered smooth. By slightly introducing regular
imperfections along the surface, more seams perhaps, I wonder if a paintball would no longer be considered smooth. It would probably be a pain to manufacture though.

[Croix71]

Agree with ya there, would the benefit worth the cost.

[ShooterJM]

Originally posted by Croix71
Agree with ya there, would the benefit worth the cost.

Well I'm working on that cost thing. Have a meeting next monday to get some more information on manufacturing costs, etc. Actually I even have phase one venture capital if I can figure out just two more things.

[AGD]

The Magnus effect as you are describing affects spinning spheres. Most paintballs fired from markers have little spin and when they do it is usually not enough to distort the airflow enough in a particular direction. The testing we have done shows that the small induced spin on paintballs does not correlate with where it hits the target when the spin is below 6000 rpm.

AGD