Increasing car efficiency by rerouting airflow?

[rumborak]

This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible.

The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car.
Could one upscale a supercharger, I.e. a compressor, to consume all the incident airflow hitting the front of the car, compress it, route it through the car, and in the back expel it again?
Intuitively this should reduce air drag, since a much smaller section of the car is now "visible" to the air.
However, the compression and the associated own air drag might thwart the energy balance, making it negative overall. But, is that necessarily so?

 

[berkeman]

This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible.

The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car.
Could one upscale a supercharger, I.e. a compressor, to consume all the incident airflow hitting the front of the car, compress it, route it through the car, and in the back expel it again?
Intuitively this should reduce air drag, since a much smaller section of the car is now "visible" to the air.
However, the compression and the associated own air drag might thwart the energy balance, making it negative overall. But, is that necessarily so?

For your back-of-the-napkin calculation, figure out how many horsepower it would require to do that air pumping, and compare that to the power wasted in the excess air resistance...

EDIT -- Wait, you can write on both sides of a napkin, but only on one side of a used envelope...

 

[sophiecentaur]

how many horsepower it would require to do that air pumping,

Yes - the pump would have to be free of turbulence.

 

[mrspeedybob]

Sounds like you're essentially talking about a jet engine designed to generate just enough thrust to cancel out it's own drag, rendering the latter effectively zero.

 

[sophiecentaur]

Sounds like you're essentially talking about a jet engine designed to generate just enough thrust to cancel out it's own drag, rendering the latter effectively zero.

. . . . . which would cost a fortune to buy and to run, of course.
The aerodynamic design of modern fast cars does exactly what the title of the thread suggests.
On a parallel topic, I have read that the skins of dolphins has small ridges and valleys all over it and is 'deliberately' flexible, which is thought to improve its hydrodynamic efficiency. I wasn't aware of an equivalent in air (but who knows what birds' feathers do for efficiency?) but http://msbusiness.com/2007/12/entrepreneur-mimics-dolphin-skin-for-fuel-efficiency-enhancement/ which mentions the subject. There are dozens of other links about dolphin swimming efficiency being higher than you'd expect.