Aerodynamics of a Car

[gtpornstar]

Especially interested in Hatchbacks.
I have a Glanza and have just lost my wing, so looking at a replacement and wondering about air flow around the car and how it can be improved.

Air canards, flow in the engine bay, rear diffusers, too much wing.

All things that i am trying to understand. Any help or direction to material is much appreciated !

[RS13]

Basically, at high speed, as the air going over the car is having to travel faster than the air moving under the car, you're creating positive and negative pressure areas, similar to the wing of an aeroplane.. hence creating lift, and this is why so much work goes into spoilers!

As the rear of any car (hatchbacks especially) has a large area of negative pressure as the airflow drops off the roof, you're getting a large lift force at the rear of the car, which doesn't help rear end traction at high speed, and this is why your car (particularly sporty models, cars often driven fast) had a spoiler at the top of the hatch.

The spoiler is designed to direct airflow over and away from this negative pressure area, reducing lift.. but also increasing drag.

I would say the factory rear spoiler was designed with many, many hours of wind tunnel testing to get it in the best location for your car, I wouldn't mess with it.

Canards.. as that air moves under the car, creating positive pressure, it also hits everything that sticks out from underneath your car, creating parasitic drag.. engine, gearbox, diff etc. Which slows you down.

You'll notice most high-speed cars have a deep chin spoiler (or "front kit", lol), the idea behind that is that the airflow is deflected down the sides of the car, rather than underneath. Canards are just there to assist the airflow up and away, (away from the vortices created by the wheels as well!) you won't get much improvement if you just stick them on a factory bumper, you need a well-designed front spoiler to get the airflow to them first, to make them worthwhile.

[RS13]

Oh, and rear diffusers.. they use Venturi principle to reduce the positive pressure at the rear underside of the car, reducing the pressure differential between the positive underneath and the negative above, meaning you get more downforce and grip in the rear.

Here's a good site to get a better picture!

http://www.autozine.org/technical_schoo ... h_aero.htm