Explain Fluid Dynamics Behavior for the Fig. Below

In the case shown the rod would try to rise.

It would also twist, unless it was traveling along the equator, _{(Of course, we all know what the orientation of the rod to equator wolud be, right}) then it would fly straight.

A ball is not subject to twisting owing to its perfect mass distribution around its center.

.................................................................................I forgot what the question was...............................

Just ignore this, I mis-read the question.

Bullet trajectory is a different animal. For one thing, very seldom will a bullet have the same diameter along its entire length.

probably not..

What you are describing is what a spinning rifle-bullet experiences, i.e. no Magnus effect*, because all areas on the cylinder's curved side experience the same friction and air (fluid) speed, while the Magnus effect is a result of a difference in those.

It would be pretty bad if you aimed straight and the bullet veered off due to old Magnus...

*SIDE WINDS (excluded for this discussion) do affect spinning projectiles with a Magnus force, but the spin also provides gyroscopic stability.

Exactly !! the question was raised after seeing a spinning rifle-bullet.

sir can you please guide me where would i find theoretical analysis on spinning rifle-bullet ? i want to learn difference between spinning bullet and steady bullet and get theoretical knowledge on there efficiency.

i've referred few fluid mechanics books but i didn't find the case where fluid flow direction is as shown in the attached figure (or reference to spinning bullet)

as i was curious about it, i just prepared a model and done analysis on ANSYS 13 Fluent software where i found out that, spinning model shown 3-6% less Cd at different RPM than a steady model.

please tell me very can i get theory behind the Dynamics of spinning rifle bullet sir.

thank you.

So is your question directed only towards the bullet?

This would probably be a case of the Magnus effect.

At least thats what they say here.

http://en.wikipedia.org/wiki/Magnus_effect

There will be much more in the internet. Which searches did you try already?

Need to read that wikipedia article carefully; it says the Magnus effect develops only from cross-winds or yaw, where the air flow is not exactly along the axis of the bullet, and the portion of air flow that is perpendicular to the bullet axis will cause a small Magus effect.

The question above specified the flow being along the axis of the cylinder... so no Magnus effect for this case.

thanks for responding sir..

this is the point where i was struck sir..

link says that we need to consider magnus effect whn a bullet is fired at an angle..

should we consider it as "negligible magnus effect" or "no Magnus effect"

If the flow is exactly as in your original question, i.e. 100% along the cylinder axis, then there should be no Magnus effect since the cylinder experiences the same fluid interaction everywhere around its spinning envelope.

When there is an angle between the flow and the axis of spin, you can break the flow vector into parallel and perpendicular components, relative to the cylinder axis, and the perpendicular component of flow will create the Magnus effect, per available equations.

May I ask about your age and country of residence?

that was pretty clear.. thank you sir..

by the way i'm kanney, 23 years old from India.

This paper on drag crisis may shed some light on your question.

Just googling gyroscopic stability in bullets ?:http://www.nennstiel-ruprecht.de/bullfly/gyrocond.htm

Here is a link to a site called "How Bullets Fly"

It looks very comprehensive....

Ferquiza beat me to it!

thank you.. that was very helpful.

now i wanna know how would these equations change when water is the medium instead of air???

thanks in advance :)

We've already gone over this once:

Hydrodynamics

It's sounding too much like the children's game 20 questions.