I'm too much of a knucklehead to be able to copy a Google link instead of re-downloading the PDF, but here are your search terms:
- Session-3-1-Jeff-Howell-Summary-of-university-dindings-Wheel-Wheelarch-drag
- Numerical simulation of the flow around the wheel within wheelhouse - Sasan_Sarmast_Jan2010
You could do worse than mimic Porsche:
http://www.bombaydigital.com/boxster/projects/radiator/