[aerohead]

I haven't checked online for availability ,but you need to check out both of the above mentioned fluid dynamic flow loss phenomena.
The hard edges of each opening will effectively pinch off the air volume available to move through each of the slits.
Ideally,you wouldn't want anything in the airstream more restrictive than 1/4-inch hardware cloth.
One proper single opening will have the minimum drag compared to a series of smaller openings.
This is exactly why I chose the trashcan lid and bullet valve for the T-100.You'll see them used in hydroelectric plants where Pelton-wheel turbines are used,and if you've seen the recent movie 'Red Tails',you'll see therm on the tail end of the Me 262' Junkers Jumo 004 turbo jet engine's exhaust pipes.