dimples re automotive aerodynamics

does anyone know the approximate size for dimples on the trailing surfaces of automobiles?
I'm thinking about trying a hexagonal mesh made out of rope to introduce turbulence for the rear window. any ideas about sizes?
would roughly applied paint improve the boundary layer?

 

[jmw]

Interesting question. I assume you are thinking about improving the air flow the way the dimples in a golf ball work.
This was one i thought about some time ago (idly, I'm afraid) and i concluded that you have dimples on a golf ball because you can't control the airflow direction. On a car i would guess that a sequence of grooves might be better as the air flow direction is known. Size and geometry? i didn't get that far but i guessed that having a car that looked like some one built the back end out of corrugated steel might not be attractive. ACtually with a set of full profile grooves that make it look like a bellows, it may also act as a crumple zone.
I'll be interested to see what others say (who know better than me)

 

[sciguyjim]

You can probably find some info if you investigate airfoil aerodynamics. Years ago when I was flying radio controlled airplanes I came across this type of info for the airflow over wings. As I recall, the ridges (running parallel to the wing spar) would, in this case, be about the thickness of the mylar plastic used to cover the plane. What this does is create turbulence so the laminar airflow can detach from the surface.

Another thing I read about was putting grooves in the upper rear area of the wing where a vacuum would pull in turbulent air which had detached from the laminar flow over the wing. The effect of this was to keep the laminar flow from detaching before this point.