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Hi All,
I think the issue with turbulators/dimples/VG's is that the air has to be making a big turn in an area of thin high energy boundary layer. In the ball, the air is pushed out, but for best drag has to make a big change in direction to stay laminar. There is energy in the compressed boundary layer which is used to turn the air, by the dimples.
Similarly with ebdso's finding on the upper third of the A pillar. The air is shooting sideways across the windshield, and has to make a big turn to go laminar down the side of the car. Without the turbulator, this sideways air will just roll, and propagate a big vortex out away from the side of the car as it reenters the slipstream direction. With the turbulator the air tumbles and quickly becomes laminar down the side of the car.
By the way, anybody who says a Prius is good enough aerodynamic wise, was not driving head-on into 30 (thursday) and 50 (friday) mph winds here in the Chicagoland area this week.
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