How do racing cars use aerodynamic ground effect?

Question

My understanding is that ground effect works when the ground or other surface interrupts the downdraft thereby reducing aerodynamic drag.

With cars, it seems that the explanations I've found describe using the car's body itself as a wing and creating a venturi between the bottom surface of the car and the track. However, with a car the aerofoil's "downdraft" is going upwards so there's no surface to interact with it. In this case there wouldn't be any ground effect.

Am I misunderstanding this? How does ground effect work in a car which is producing downforce rather than a aircraft where it produces additional lift?

Answer 1

A simplistic way to think about this is that the wing is shoving air from one side to the other. This creates higher and lower pressure regions around the wing that cause lift (higher pressure below on a plane, higher pressure above on a car).

If you put the ground under an airplane wing, the air "builds up" under the wing because it can't disperse as easily. This allows the pressure to build up higher than it would otherwise. The greater difference means greater lift over the area of the wing.

If you put the ground under a car wing, the low-pressure region can't be filled in by air easily because the ground is in the way. This lets the pressure be lower than it would in a free-stream flow. The "lift" generated from the pressure differential is greater.