Quote:
Originally Posted by AXMonster
How about the idea of incorporating a rear slot just after the roof to rear window transition point to direct the flow coming off the roof (in an attempt to keep it moving down the rear screen) & reduce the low pressure area behind the car? Could it work?
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Yes, but how well? My concern is the volume of air that is needed to actually reenergize the boundary layer. I can't even begin to imagine what is necessary, but it is probably fairly high.
There are three sources of air that I can think up of:
1.) Exhaust
2.) Ducting high pressure air from the front of the car to the rear
3.) Electric pump
The exhaust will not provide enough flow in the average economy car. I know some F1 cars use the techique during acceleration to create a type of "blown flap" for down force. Every bit counts, though.
Ducting has been tried in the past, but from what I've read the benefits are extremely minimal or non-existant.
The electric pump shows the greatest hope, but it is going to be an energy hog. Jets that used blown flaps (the same concept) used compressor bleed air from their engine. Supposedly the engines lost the majority of their power when that was done, but it wasn't a concern since they were only used for landing.
I believe sailplanes that are trying to use the technology are doing feasibility tests to see what the system weight is going to be. Something like 500 watts of solar panels need to be added, in addition to a pump. 500 watts seems minimal to a car, but a sailplane is much less draggy and therefore needs to reenergize the BL much less. A hatchback will probably need much more power.
Lastly, if you do undertake this challenge, make sure that the intake air to the blower is used for effect...might as well evacuate some of the high pressure air on the front of the car.
In closing, I would say the idea is feasible but it rates high on the cost/benefit ratio list. It would be cheaper to build a boattail, but a hell of a lot less cool/innovative.
- LostCause