Using Power to improve Aerodynamics

[CFECO]

This has probably been discussed before, but I could not find it, sorry if I missed it. Has anyone ever done any studies on what would happen if you took a blower, and sucked air out from under a vehicle, or from the high pressure area at the front, and blew it out into the wake area at the rear, basically "Filling The Vacuum" ?

[Fat Charlie]

Heh. Back in the 80s Car & Driver did a road test on a riding mower. They described the downforce package (underbody fan) in great detail, concluding that the air collecting bag was a bad idea because when operated offroad, it quickly became filled with crushed vegetation. That deficiency, and the rig's low top speed made themagazine question the need for a downforce generator like that.

[CFECO]

My thought was not for downforce, but Drag reduction. Pull air from where we don't want it, high pressure areas, and vent it into the low pressure, wake area at the rear.

[Fat Charlie]

You're trying to do something that occurs naturally, only better, and by using power... in an effort to reduce power usage.

If it were an effort to increase downforce or top speed, then by all means- that's using energy to create a desired effect. But if the desired effect is less energy loss, I think this is the wrong way to go.

[Smokeduv]

Many years ago, like at late 70's if I'm not mistaken, some racing teams wanted to exploit just that. The first successful one was the Chaparral 2J, which had a 2-stroke engine from a snowmobile, I think, and connected to 2 big fans from a military tank and then they sealed the sides with skirts. It wasn't very successful because of reliability issues, but it was competitive when it was running.

Some years later, that concept was taken into F1, where the Brabham team put an enormous fan behind the car (The Brabham BT46B or "fan car"), which they said it was to cool the engine, but it was ducted in a way that half of it cooled the engine and the other half sucked the car. The fan was connected to the engine, so the higher the revs, the more the suction. The advantage was so huge that it was banned (that and because the other teams complained, so they withdraw and the next year the rules were changed to ban moving aerodynamic parts). It only ran in just one grand prix, which it won by a very big margin.

For ecomodding purposes, it may work, but as in the Chaparral, I don't think it's going to be easy, or cheap, or reliable and might be too heavy.

[CFECO]

It would be a trade-off for sure, but would it be better or worse overall, that's the question. We know at higher speeds, Aero Drag is the main fuel user, and since the engines are not being used in their most efficient operating range most of the time, WOT under load, adding load to help aero "might" be good.

[aerohead]

It's been considered since Prandtl's blown/suctioned wing research of the 1920s.
Georgia Tech continues research on it after decades of work.
So far,more energy is expended in moving the necessary volumes of air,than is saved with the modification.Also,the equipment can breakdown,something a streamlined shape cannot suffer.
The Ferrari 599XX race car has an intermittantly-used,porous, suctioned diffuser,enabled by two-trunk-mounted electric blowers which suck air from under and blow it cyclically through the taillights to detach the wake.
Together,all the 599XX mods drop the car to Cd 0.285,compared to Cd 0.336 for the base 599GTB.
Cd 0.285 is a long way from VW's passive,Cd 0.14 'flow body' of 1981.