If you are watching the Olympics, have you noticed those body suits that the swimmers are wearing?
Those suits are called "shark skin" suits, and were only declared legal days before the Sydney Olympics. Any swimmer with Speedo, TYR, or Arena as a sponsor has to wear them, but the swimmers like them. But what's the big deal?
Well, they are covered with patterns of "ridglets" and dimples determined by fluid dynamic modeling and patterned after - surprise - shark skin. The same idea was used in the America's Cup in 1987, on the winning hull, and was so fast that this texturing was banned.
Another version is used on US Navy attack submarines, but patterned more on the characteristics of dolphins, which use different hydrodynamic properties to achieve their speed and efficiency.
The ridglets or ribbing are intended to reduce skin friction by capturing air and reducing surface area. When you see the suits glistening with bubbles in underwater videos, the suits appear to be working. If the slots are to small or too large, it backfires and increases surface area.
The dimpled areas are intended to reduce pressure drag, similar to cavitation, that occurs over irregular shapes, like eyebrows and chins, even the curve of hipbones or breasts. Placed in the right spots, the dimples create a little turbulence instead of a vacuum at those places.
Sponsors claim up to 4% improvement in drag, but others disagree, and point out that swimmers are relatively slow and thrashing compared to sharks or boats. Physiologists are waiting for Olympic results. Statistics should show a detectable blip in resulting times of suit wearers are actually improved.
Discussion distilled from a Special Section of the journal Science, 30 July 2004.