Re: How to estimate air flow &velocity thru a rotating ram air scoop

Your question is not very clear but maybe I have at least a partial answer.
You have a short hollow cylinder 4 inches diameter, 2 inches long, rotating
at 500 rpm. You want a scoop 3/4 inch high by 1 1/2 wide to provide maximum
airflow but you say nothing about conditions inside the cylinder.


A natural thing to do would be to position the scoop tangent to the outer
edge of the cylinder. This maximizes the relative air velocity. 
Velocity at
the outer edge is:

Vtip = 500 x pi x 4 inches per minute 

also = 6,283 inches per minute or 523.6 feet per second

Scoop area is 0.75 x 1.5 = 1.125 square inches or .0078 square feet. 

Amount of air taken in is 4.092 cubic feet per second. 

To minimize entrance losses, the slope should match the relative velocity at
the outer edge. This is not possible to determine without more information.

A better design for the scoop would be one with variable slope, greater as
the radius decreases. This would be similar in contour to a shrouded
propeller blade.