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Originally Posted by dhehnke
I'm not sure what you mean by this. As far as improving aerodynamics on a blunt rear end of a car, are you saying a wing-like structure doesn't help? I find this hard to believe when you can find small versions of this on a huge portion of modern SUVs and other boxy rear ended cars. I can't see them spending money on this if it didn't work.
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Many of today's SUV rear extensions merely elongate the roofline profile,allowing a little more pressure recovery before separation occurs.They also provide some shade and keep snow off some of the backlight.
As to airfoil-like structures,Wolf H. Hucho,who ran Volkswagen's climatic wind tunnel for a decade,and who continues to publish textbooks on road vehicle aerodynamics,has reported that airfoil-like structures which DID reduce drag on aircraft,or projectiles,failed to reduce drag when placed on road vehicles.Not even NASA, will attempt to use wing sections on a road vehicle.
Again,the only structures which have proven drag reducing capabilities,are either box cavities, boat-tails,or blown/suctioned slots.
And since,statistically,a road vehicle will be driving in 7-mph wind spectra most of the time,you cannot rely on the drag characteristics of a fixed angle-of-attack airfoil,operating in a dynamic flow environment.
A look at Abbott and Von Doenhoff's book on airfoil sections will show clearly reveal the evidence.
Hucho is adamant about only simple,separation-free elongation of the aft-body being effective towards streamlining.