Chunky wrote:
Dimples DON'T create drag. If they did, golf balls would be smooth. They promote separation of the airflow and as I said, reduce parasitic drag. This is sometimes called "skin friction" drag. Basically, if the surface is very smooth, the airflow stays attached to it for too long and causes high drag behind the point where it detatches.
Some aircraft wing designs use devices to deliberately separte the airflow at a point beyond that where it has done its job. So-called "turbulator strips" are an example. I don't doubt that F1 cars employ a similar approach at some places on the bodywork.
Like I said, there are several different explanations of why dimples work and it is a bit like "how can bumble bees fly". The reality is probably a combination of all the common explanations added together rather than just one of them being absolutely right.
For a simple surface, whether smoothness or some variation of roughness will give the lowest drag depends on a lot of things like the geometry and the topography of the surface. Golf balls are a simple geometry, F1 cars are much, much more complex.
In general terms, you would want part of an F1 car to be smooth rather than covered in lumpy, bumpy rubber grime (hence the reason why they clean them so meticulously). But there are other areas where the sharkskin approach would give benefits, if only it didn't provide such a wonderful sticking place for all the airborn corruption that the car drives through over a two hour race.
As another example of how things can change during the course of a race (or flight), you can even get devices that wind out along aircraft wings to scrape off the bugs that you would pick up during flight - these prevent a very marked deterioration in performance in the height of summer.
Hello. Just thought I would clarify this explanation as I see some misconceptions here. (I have a Masters Degree in Aerodynamics).
There are two components to drag (skin friction and pressure drag). Skin friction is, as the name implies, drag created by friction between the surface of the material and the air molecules. Having a smooth surface reduces the skin friction drag.
Pressure drag is related to the fact that when objects travel through the air, they leave a region of low pressure air behind them. High pressure in front + low pressure behind means that there is a net force acting and this is what we call pressure drag.

The reason why dimples are used on golf balls is because they promote transition of the boundary layer from laminar to turbulent. The boundary layer is the region of air close to the surface where the velocity of the air particle changes from zero (at the surface itself) to the free stream velocity (the velocity of the free air travelling past the golf ball). A laminar boundary layer separates easily (top). The turbulent boundary layer does not separate as easily (bottom). This delayed separation leads to a thinner wake, which reduces the area of low pressure and hence the pressure drag. This reduction is greater than the gain in skin friction drag for the golf ball case, and therefore you have a net reduction in drag.
For F1, dimples are not used because given the high Reynolds number of the flow around the car (the Reynolds number is a ratio between inertial and viscous forces) the boundary layer will naturally transition to becoming turbulent almost immediately (the flow around a golf ball on the other hand has low Reynolds numbers and thus dimples are used to "force" the transition). Furthermore, the flow of an F1 car is significantly more complicated and designs will make use of 3D flow structures like vortices to work the air which can greatly affect the tendency of boundary layers to separate.
On aircraft, you never want the airflow to separate from the wing at any point (that is stall). Vortex generators (turbulator strips) are used for two reasons:
1. To re-energize the boundary layer (to prevent stall). It does this because the formed vortex (which is like swirling air), will draw in high energy air from the free-stream which then increases the overall energy of the boundary layer, thus preventing it from separating.
2. Sometimes used on swept wings to prevent spanwise flow (i.e. migration of air from the root to the tip), this is also in order to prevent stall (swept wing designs can suffer from some unrecoverable stall states if "fences" are not used).
Hope this helps
