Quote:
Originally Posted by winkosmosis
It's not just the mass either though. Moving air takes energy, because air is surrounded by air. Pushing air out of the way of a vehicle means shoving air molecules into other air molecules. It takes energy just like moving air with a fan takes energy.
A more gradual transition is good in the same way a shallower raked windshield is good-- air is moved more slowly relative to the speed of the vehicle.
Look at your vehicle's electric cooling fan. See how the blades are curved? Why don't they just use the flow departure angle for the whole blade and make it flat?
Because it takes less energy to ramp up their air speed gradually over the blade surface, from a shallow angle to a steep angle.
We need to put to rest this nonsense about attached flow being the end all be all except at supersonic speed. A normal fan doesn't spin at supersonic speed.
 |
a general rule of thumb: moving alot of air slowly is more efficient than moving a little bit of air quickly. that's the reason why helicopter rotors are as big as they are