I know just enough about this to be dangerous. I hope someone with true knowledge can expand upon the matter.
OK, you asked
for it.
Dimples are just another type of vortex generator. As on a wing, they induce turbulent flow in order to keep the flow stuck to the surface as far as possible on the 'back' side of the body. This results in a reduction in the size of the low pressure region on the backside as the high pressure flow wraps further around the body. With less area of low pressure behind it, the difference in forces on the body from front to back is also reduced. This differential pressure force pushing back on the body in the direction of the flow is thus known as 'pressure drag.'
On a body that is fixed in orientation to the flow, like cars and planes (well - most of the time anyway
), the VG's are useful only in certain places on the body. A golf ball spins in flight, so the dimples are placed all over the body so they are where-when they need to be.
Part of my senior project was going to be testing the drag reduction from various configurations and locations of 'dimple tape' on a typical strut section in the low speed wind tunnel, so I did some research into what was already known. Unfortunately, the project turned into a wind tunnel flow field survey to check the wind tunnel itself. We ran out of time for the dimple test.
