Quote:
Originally Posted by freebeard
aerohead -- Thanks for giving this your attention. I'm looking at a die-cast scale model and it looks like a [no more than] 4" inverted U-shape leading edge for an airfoil.
Given, say, 250cfs of flow (25 times 10x) through the duct what should it's area be? I'd address the slot opening later.
I'm comparing a minimalist vertical hoop with something more like the Bird of Prey:
 https://nationalinterest.org/sites/d...s/boeing_0.jpg
I think it could have an angled intake throat if the plenum is fed from the quarter-points instead of the ends. |
I'd have you look at ASHRAE and SMACNA, and consider your duct shape and surface roughness.
Friction 'pumping' losses will be a Reynolds number function, based on how smooth the duct surface walls, at a given flow velocity.
You'll see at SMACNA, that your losses vary remarkably with flow velocity.
You're at 15,000 CFM. Choose a loss factor to establish design velocity. Then dividing your volume by velocity will spit out the area.
It's very conditional.
The smoothest surface has a friction loss coefficient of 0.003 pounds/ sq-ft.
Your design velocity, in feet/minute, will give you your surface area.
I don't have the proper work books with me to go any further. I'll get that for Friday.
On a car, the surface area is approximately 10-X projected frontal area, making a frontal area-based friction drag coefficient = 10 X 0.003 = Cdf 0.03. Total drag, minus 0.03 = approx. pressure drag.
[Dynamic pressure ( 1/2 x rho x velocity-squared ) x Cdf ]= friction drag component.