View Single Post
Old 01-20-2013, 11:31 PM   #41
Shankenstein
Frosty Carrot
 
Shankenstein's Avatar
 
Join Date: Jan 2013
Drives: The Atomic Carrot
Location: Baltimore, MD
Posts: 513
Thanks: 272
Thanked 428 Times in 199 Posts
Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by Dimman View Post
It's the old F1/racing way, too.

Another is paint streaks, where a series of dots are painted on the car which then makes a few runs, they then look at the trails left on the car.

Analysts still use a similar technique when they can get pictures of race cars that run in wet conditions. They have very distinct streamlines left on them. They are particularly useful for analyzing inlet effectiveness.
New plan. Somebody needs to splatter paint their car for science! Volunteers? I'd bet other substances would do just fine too (like mud, ice cream, motor oil, liquid soap, etc).

I still prefer string since you can see flow separation more easily. For a given frontal cross-section (assuming it's unavoidable and constant), we can lower the drag force on the car by keeping the flow laminar and connected.

Good opportunities for drag reduction:
  • undercarriage smoothness (flat is good)
  • airflow around tires (redirect flow around them)
  • front bumper smoothness (boxy is bad)
  • exiting airflow from engine bay (smoothly reintegrate it)
  • transitions at the cowl and side mirrors
  • transitions at rear windshield and trunk (big target for flow separation)
  • reconnection of the flow paths (minimize the virtual cross-section for exiting air)
As others have suggested, under-car air speed should be as high as possible without restricting flow. High speed = low pressure. This serves to decrease drag and provide the differential pressure for Bernoulli's downforce.

Wheels will generate turbulence around them, for alot of reasons (too many to name). It's usually best to guide the airflow away from them to avoid unnecessary drag. Obviously race cars will have dedicated ducts to sent air to the brakes, and that's a different ballgame.

The rest of them are about maintaining laminar flow as much as possible. The body panels will never resemble an airfoil/teardrop, but similar concepts are still relevant. Flow should stay connected with the body panels, and body panels should never create pockets.

Side note: I realize the golf-balling a car is somewhat legit science, but good aero can generally trump bad aero+dimples. Use turbulence only when necessary.
Shankenstein is offline   Reply With Quote
The Following User Says Thank You to Shankenstein For This Useful Post:
WillRacer1jz (01-21-2013)