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Old 05-22-2019, 03:17 PM   #17 (permalink)
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Originally Posted by fastflyer View Post
I do not question the operation of a diffuser. But in a car without diffuser, put the Vortex generators. For less drag and more downforce?.

He left a DYNA study on vgs and airtabs. And how they are placed in the back of the car.

I would say that the results would be valid,only for the specific vehicles tested,exactly how they were configured, and any extrapolating of the performance equivalency to any other vehicle would be dubious.
If their numerical simulation satisfies the full Navier-Stokes equation,then I'm okay with that.
The base pressure of a vehicles wake is established by the local pressure at the 'first' separation line at the rear.The presence of VGs at the separation line would not alter that local pressure.There's no ramp behind the VGs on which the edge vortices induced by the VGs to act.I don't understand the drag reduction mechanism they purport to achieve.
It would have been more proper for MIRA to have conducted,rapid,back-to-back runs,with and without the VGs on the same vehicle,to isolate any variables between the two.I'm quite surprised that they conducted the testing in the manner in which they did.The SAE would not have allowed it.
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