modifying air flow electrically
 

I hesitate to introduce this topic, given the almost unlimited potential for snake oil that might result, but here goes anyway.

All of the aerodynamics discussed here, and in fact, pretty much everywhere else, assumes that neither the fluid nor the vehicle carries a significant charge or magnetic field. Normally this is true - but it does not have to be. For instance, charged molecules could be injected into the passing air, and then the flow as a whole redirected using magnetic or electric fields. In practice only a tiny tiny fraction of the air molecules would be charged, but that would likely still be enough to affect the flow as a whole, since the mean free path of an air molecule is very short:

DavidPace.com - Mean Free Path of Air

so that force applied to the few charged molecules would be rapidly transferred to the uncharged as well.

Imagine charged molecules are injected well before the trailing edge of the vehicle. Large electrostatic plates at the back might be able to "focus" the charged flow more inward than it would otherwise go, possibly reducing drag. Indeed, simply charging the air on top of the car positively, and the air under the car negatively, would produce a force to pull the two streams together which would otherwise not be present (this is very much preliminary hand waving, there may well be no pair of oppositely charged atmospheric ions available for this purpose which are safe to inject into the air at the requisite concentrations). Whether any of these approaches ended up being a net win in terms of energy usage would of course depend on how much (if at all) drag was reduced, versus the power needed to generate the charge and maintain the electrostatics or magnets. Of course, none of this is likely to work in the rain.

Some related ideas have been out for a while, although they are usually applied at much higher velocities than are seen on a car. See for instance:

AGT - Plasma Aerodynamics
Will Plasma Revolutionize Aircraft Design

I have read some articles on plasma aerodynamics, and the theory is sound - it has been successfully demonstrated and performed extremely well IIRC but never got beyond that, in much the same way that laminar flow wings were tested in the X-Plane series back in the '50s and '60's but never got beyond the experimental stage because the technology was too maintenance intensive for the day.

you might be surprised at just how far along the air force got back then - if even half the things they tested were allowed to flourish we would have a manned mars outpost by now.

That's some out of the box thinking! IANAPP (I am not a plasma physicist, although I have a bachelor's degree in physics), but I thought I'd mention a few things to think about:

1) It takes some power to generate the ions/plasma and disperse it. Generally, this will scale with the amount of current you need to get enough ions in the air to make it react as you want. I don't think the room ionizers use much power, but moving down the road means you are trying to inject ions into a very large volume, so the power required is significantly more.

2) Generating a stong magnetic field electrically takes a lot of power (--> high load on your alterntor), but perhaps a configuration of permanent magnets could be used to guide the plasma flow. However, permanent magnets would not be easily tuned for different vehicle speeds.

3) Static charges need to be properly dissapated so they don't build up and cause a safety issue or equipment failure.

4) Plasma wind might block your radio reception (although I'm guessing that the level of ionization contemplated here would not affect it too much)

5) Plasmas can be induced to emit sound... imagine a vehicle-size subwoofer!:cool: