rounded aft wheel well edge?
 

after comparing some CFG images found online, it would appear as though generally there's quite a lot of air exiting the front wheelwell on the underbody, this makes sence as the wheel leaves a low pressure areas wich sucks the air our, wich gets trapped in the wheelwell... this doesn't look like a very desirable situation, and a lot of small dam designs in front of the wheelhell seems to sugest keeping air out of the well is quite important... however likely quite a portion of this air might get in there trough the grill.

now to get to my question, would it be a good idea to round the transition of the wheelwell to the underbody? perhaps by adding a quart section of a plastic pipe, or some flexible material that's curved backwards?

in theory you'd want to make an exit duct i guess like some racecars, but since it's not practical to hack up your car for most of us perhaps there's some gains to be squeezed out of this with a fairly simple mod.

also perhaps small vanes behind the tire and wheellwell could straighten out this flow and reduce drag even further?

Not quite what you're talking about, but similar. The rear edge of the front wheel well is curved in for smoother airflow.
http://www.edmunds.com/pictures/VEHI...55-300x189.jpg

Kind of like the first generation Insight did along the side of the car, a nice rounding. I had not thought about it to the bottom, but it may help. As far as the veins go, there are some general rules that should be followed to transition turbulent flow back to laminar. If I remember correctly (this is a big if), you need a tube (or grate) that is AT LEAST twice as long as it is in diameter. We had a setup we used that would create turbulent flow in one section, but before getting to the next we had to have good laminar flow again, so we used straws bundled together. I don't know if the same rule applies to spacing between vanes, or if it works on a larger scale than straw-diameter tubes (which would not be practical for cars with road grime).

something like that at the bottom

the shape of the insight should be on every car as the upper rear "corner" of a wheelwell seems to be the place where a lot of air exits, unfortunately traditionally the shape is more scoop like then exit like.... fender vents and something like the insight might be a good thing

this image i googled up shows both airstreams....
http://i77.photobucket.com/albums/j5...6c4264_074.jpg

both seem to be fed by the font grill... this might explain in part why a front grill block is so effective... it will reduce these turbulent streams wich will also effect the rest of the wake i think

rounded
 

Remember,the forward stagnation pressure is communicated through the cooling system,and as soon as the air passes the heat exchangers it's going to "look" for a way out.That speeding low pressure air along the side of the car is the first candidate if the under hood air can get to it.------- You can design for that like Kamm and Morelli,or you can move the entire cooling system to the rear like Ford did with the Probe series concepts.

The NA Miata has angled inward and radiused panels behind the front wheels


http://img.photobucket.com/albums/v9...g/ShortLip.jpg

The wheel arches look angled inward at both the leading and trailing edges around all the wheels. Isn't that just a body style thing?

first gen miatas (with the pop up headlights) apperently had the insight style wheel wells
http://i77.photobucket.com/albums/j5...ay/90Miata.jpg
laters models seemed to have a more conventional flattened edge.

lunarhighway's pic shows it better. Only the rear edge of the front wheelwells