Shark species that can hurtle through the ocean at high speed—up to 80 km per hour (50 mph)1 —have a number of special features that allow them to do that, e.g., the tiny scales on the surface of their skin.

Each scale is just 0.2 mm (0.008 inch) long and is made of tough enamel—if you touch shark skin it feels like rough sandpaper. You might at first think that a perfectly smooth surface would be better for speed but in fact it’s been known for some time that the scales actually reduce drag.2 And now researchers have discovered another special characteristic of shark skin. In light of evidence that some shark species may bristle their scales during fast swimming, engineers decided to see how lifting the scales on end affects water flow over the shark.

Using models of bristled shark skin in a water tunnel experiment, researchers from the University of Alabama’s Aerospace Engineering and Mechanics Department and their colleagues observed that at high speed, tiny vortices or whirlpools formed within the cavities between the scales.3 (The scales were raised at an angle of 90º to the surface of the skin.) The effect of these vortices was to form a kind of ‘buffer layer’ between the fast moving fluid and the skin’s surface, thus preventing a turbulent wake from forming behind the shark. In other words, reducing drag….

 

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