Credit: Haecheon Choi, Parviz Moin and John Kim

V-SHAPED GROOVES called riblets (above) have been found to inhibit the motion of eddies, thereby lessening the drag they can exert on an aircraft's wing. A cross section of the airflow over the grooves (above, right) shows the vorticity contours--warm colors are clockwise, and cool colors are counterclockwise. The arrows are velocity vectors for the flow over the riblets. To be effective, the riblets must be very closely spaced, like phonograph grooves. The skin of a shark has tiny, toothlike denticles (photomicrographs below ) that seem to serve the same function as the riblets, lessening the drag on the creatures as they move through the water.

Credit: Wolf-Ernst Reif