Interesting Slide Show about Aerodynamics and Car Design

Functional air scoops are a little more than holes punched in the exterior. They could also be there on high performance cars for brake cooling, not aero improvement.

 

A better solution would be to mount a pair of conformal vanes or ducts on either the bumper cover or front quarter panels. The bumper cover because it can be replaced. Compliment it by doing careful benchmarks and air stream, tuff testing. One risk is making an accidental reed or whistle.

I admire the initiative to propose it. You might consider joining ecomodder.com or their forum that includes a percentage of home experimentalists.

Bob Wilson

 

Before modifying the wheel well you should do a little research as to whether the alterations will impact the crumple zones that are part of what makes the car safe. I have no idea how you would do that.

 

Lots of cars and trucks now have air curtain ducts: they reduce the yaw angle of flow exiting the wheel housings. You can read more about them in Aerodynamics of Road Vehicles (ed. Thomas Schuetz, SAE 2016) pp. 329-330 (Schuetz is an engineer at BMW, which developed the first production air curtains for the 2012 3-series).

As far as adding things to your own car: yes you can! Just don't guess at it; airflows are immensely complex and not intuitive and you will most likely guess wrong. You will need to test and measure: tape tufts to your car to see airflow directions and areas of attached or separated flow; measure panel pressures with disks taped to body panels; measure changes in lift using ride height sensors; measure changes in drag by coastdown testing (if you can get it to work; you have to be careful with this technique because it can be subject to huge error).

Tuft testing
Measuring aerodynamic pressures
Coastdown testing
Using the above to modify the spoiler on a Prius



Testing fins for stability on a Prius



I added external ducts to the front and rear wheels (you can see them in the image above). As @bwilson4web suggests, external ducts are much easier to build and test than internal. Front ducts made the car more stable in crosswinds. Rear ducts increased pressure on the bumper cover sides behind the rear wheel openings, an indicator that flow is better attached there.

My 1991 Toyota pickup is more interesting than the Prius, since the mechanical throttle connection makes it possible to measure changes in drag using throttle-stop testing:

Mirror removal and grill block
Air dam
Wheel covers
Tailgate spoiler