View Single Post
Old 03-21-2014, 06:55 PM   #363 (permalink)
aerohead
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,228
Thanks: 24,375
Thanked 7,357 Times in 4,757 Posts
air speed

Quote:
Originally Posted by CFECO View Post
At what speed are all these tests done? I'd think if the air was going 100 mph the flow would be much different than if it was going ten MPH. Without knowing the speed for each test photo, they are basically meaningless.
For the lengths of contemporary automobiles,the turbulent boundary layer and Cd are established at around 20-mph and remain constant up to around 250-mph,when compressibility affects kick in.
So a smoke trace photo would look essentially the same between 20,and 200+ mph.
Since the electric motors powering the wind tunnels can be in the thousands of horsepower range,the lower the test section velocity,the more economical the operation.And you can imagine the volume of smoke necessary to even show up at high tunnel velocities.
In the testing section of Hucho's books he shows the specifications of most leading automotive wind tunnels.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following 2 Users Say Thank You to aerohead For This Useful Post:
CFECO (03-29-2014), mikeyjd (04-01-2014)