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Old 11-01-2009, 07:08 AM   #27 (permalink)
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Originally Posted by majestic View Post
... only where you have flow separation, would these dimples or any kind of vortex generator help. On most sedans, the back glass is prone to flow separation, and so you may see some reduction in drag there if implemented right. The rest of the car should have attached flow and thus the dimples would only add skin friction drag.
Thanks, majestic.

OK, so based on this understanding you could cover the rear glass with dimples and the separation would be delayed, with a reduction in net c/d. Nice.

However -
1) You need to be able to see through the glass.
So we need researchers to develop 'glass' with an index of refraction identical to air (zero??) so the bubbles won't affect your view.

2) The worst offenders in the rear wake department generally are the vehicles with a non-sloping roof: vans, wagons or hatches with a near-vertical rear panel. It looks like dimples won't help them much. You could put the dimples along the rear edge, like vortex generators, but you're not delaying the separation to occur at a point with a smaller cross section to get a smaller wake.

Does that seem right?
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