I’ve searched the internet for a long time for hard data on ground effects diffuser design. Finally I found what I thought was a gold mine: Ground Effects Aerodynamics of Race Cars.
SITE:http://eprints.soton.ac.uk/42969/1/GetPDFServlet.pdf
Actually it’s a review of many ground effects...
On an enclosed body race car I am designing a diffuser for ground effects. Because of the bodywork, there is no source of high speed flowing over the trailing edge of the diffuser. This is an important feature for entraining air out of diffusers and enhancing the flow. I plan on introducing...