Wind resistance on a rapidly rotating flywheel

1. Jul 20, 2012

I am simulating a rapidly rotating (horizontal axis, if that makes a difference) flywheel. The software isn't too sophisticated w.r.t. wind resistance, unfortunately, and seems to use the diameter of the rotating body as one of the main parameters, in addition to the velocity of the rotating body. Consequently, I get pretty much the same results for a rotating disk with diameter (D) and velocity (v) as I do for my rotating flywheel with the same overall diameter and velocity.

Intuitively, the rotating thin-walled and narrow cylinder-shaped flywheel, with its lesser surface area, would be less effected by wind resistance than a solid disk of the same thickness and diameter, right? Unless there are odd turbulence effects with the cylinder shape that come into play; anyone know?

Anyway, the equation used in the software is F= -D[a(v) + b(v^2)], where a and b are the only values I can modify in that equation. Also, I can totally turn off wind resistance, but that seems to give pretty unrealistic results, and can vary the wind speed and angle w.r.t. the rotating object, although in my case, I have left these 0 to simplify things (I am not sure how these are factored in, exactly, for fixed position objects, especially round, rotating ones).

Anyway, anyone have any ideas on what I should set a and b to in F= -D[a(v) + b(v^2)] for my flywheel, or have knowledge of how wind resistance affects this sort of rotating shape? Thanks.

2. Jul 20, 2012

mikeph

Sorry, I've stopped at the second paragraph, I don't understand the difference in the two shapes. One is a cylinder shape, and another is a solid disk? Is one hollow?

3. Jul 20, 2012

CWatters

Google found this which has equations for the drag on a flywheel of thickness h. See equation 3.140..

To work it out for a hollow cylinder perhaps you could work out the drag for two solid flywheels one with radius Router and the other Rinner. Subtract one from the other to account for the hole.

4. Jul 20, 2012

MikeyW - think wagon wheel without much in the way of spokes vs. solid disk, or bike wheel vs solid disk. Since the bike/wagon wheel has less surface area, I would assume it is less impacted by wind resistance if other factors like turbulence aren't an issue.

5. Jul 20, 2012

Thanks, Cwatters. I will see if the reference helps and can be adapted to my software's limited capabilities in this area. Nice find.

6. Jul 20, 2012

AlephZero

7. Jul 20, 2012