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Old 02-15-2019, 03:41 AM   #193 (permalink)
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Originally Posted by Bicycle Bob View Post
Arrgh! Dimples are not a panacea. They are used on golf balls because their shape is so bad that another mistake can improve it. Specifically, the transition from air getting out of the way to air returning is so abrupt that the air is thrown right off, expanding the wake more, unless it has been churned up to stick on the surface. There are a few other examples of boundary layer turbulence being used to help fix a shape, but they don't get into the popular literature as a trap for the amateur.
You could have just said the only place on that car the dimples would have possibly been a benefit is the rear bumper area where there is none.

That is what I found so odd about that car.

Other than that it's general shape is very sexy and aerodynamic looking.

Originally Posted by freebeard View Post
At least the dimples are in an area where they might have some good effect. Most plaster them all over the hood and front fenders.
I agree the roof dimple location is better than hood or front fender location, but not by much.

I disagree in the roof location at all however, the gently sloping roof and rear window location chosen does not need it.

Originally Posted by Bicycle Bob View Post
If they are needed, it is usually on the front, but this shape has plenty of length to avoid abrupt transitions with. The dimples raise the skin friction considerably, while only letting the wake follow that stylish curve to the transom a few degrees farther. A conventional smooth top and sharp cutoff would be much slicker. This guy is just trying to sell his art with a false rationale.
The front is where high pressure build up occurs (adherence/attachment), dimples do not help anything there. Tripping up the air early on to then flow over the aerodynamic shape you pointed out is defeating the purpose of an aerodynamic shape with attached air flow.

Past the mid-point (high-point on aerodynamic template or in this case sphere) detachment of air occurs, the eddies (turbulent flow) caused by the dimples change the trailing air flow also known as air drag.

Both links below are excellent reading, I'm not providing the links to just reveal or credit the source of the images as I usually do. Good reading.

Surface Finishes -
why are they not used on an F1 car

Dimpled Surface Finish

Boundary Layer

I think we all recognize that the dimples on this car are a styling exercise or marketing exercise and not an aerodynamic engineering exercise.

However the what, where and why of it seems to be of debate. Hence the design is successful in beguiling us, and adding mystery.

NOTE: Attachment below is intended to illustrate that the roof does NOT need dimples to have attached flow, but the rear hindquarter may benefit from added dimples.

The reason a golf ball has dimples all over is the ball's orientation in flight cannot be guaranteed as the ball may spin. If one could maintain non-rotating flight, dimples on the aft half would help, but making it teardrop shaped for attached flow would be even better - but then it would not be a ball.
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Last edited by kach22i; 02-15-2019 at 04:39 AM..
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