That same pressure also pushes the wheels down.flynfrog wrote: air is coming out of there. THere is a high pressure area that builds up in wheel wells. not sure how the compare with slots ect but I would guess it has more to do with the required size being better as a large hole.
I did some CFD simulations of this for a conference once. Here is some of the material I put online:
Geometry A:
Geometry B: