aerohead has the best handle on this, but I would suggest that the shape doesn't "throw" air. The air is just sitting there, the car moves through it, and it tries to get back to where it was. The shape causes pressure and velocity to trade off. The velocity can have a component at right angles to the direction of travel. That probably sounds like the same thing.
Consider this:
http://ecomodder.com/forum/showthread.php/another-vortex-generator-application-2871-2.html#post88536
I found this by going to Google Images and entering <<site:ecomodder.com cfd windshield header>>. The local search only finds words [mostly]. There have been threads on open window vs air-conditioning and internal ducts. How about rear mounted radiator?
Rear Mounted rad n other trickery!
Using A-pillars as tubes to duct hot engine area/radiator air to the roof?
Aero design question
maybe you can find something in
Random Wind Tunnel and Smoke Pictures Thread . It's only 43 pages.