SHARK TRIVIA: THE LINK BETWEEN SHARK SKIN AND PROPULSION...Streamlined sharks are legendary for their effortless swimming. Coated in tooth-like DERMAL denticles, the skin is thought to behave like the dimples on a golf ball, disturbing the flow of water over the surface to reduce the drag. But something didn’t quite sit right with Lauder. ‘All of the shark skin studies were done on flat shark skin mimics that were held straight and immovable. But shark skin moves’, recalls Lauder. Lauder suggested that they take a look at the fluid dynamics of shark skin and its analogues to find out how the fish’s motion affects fluid flowing over the rough surface. Gluing pieces of shark skin together to produce a flexible foil, Oeffner repeated the swimming experiment, and this time the denticles had a dramatic effect. The intact skin foil swam 12.3% faster than a sanded, smooth skin. The shark’s rough surface improved the swimming performance spectacularly. After proving that the denticles on shark skin significantly improve the fish’s propulsion, Lauder and Oeffner were keen to find out how they affect fluid flows around the body. Returning the flexible shark skin foil to the swim tunnel, Oeffner and Lauder captured the water’s swirling motion with laser light and realised that in addition to reducing drag, the skin was actively generating THRUST. ‘That’s the number one surprise. It’s not just the drag-reducing properties, but the denticles alter the structure of flow near the shark skin in a way that enhances thrust’, explains Lauder. He is now keen to design physical models to see how altered denticle arrangements affect fluid flows over the skin and to build a computational model to tease apart the beneficial effects of the skin’s thrust and drag reduction. (Reference: Oeffner, J. and Lauder, G. V. (2012). The hydrodynamic function of shark skin and two biomimetic applications. J. Exp. Biol. 215, 785–795.)
Posted on: Wed, 15 Oct 2014 15:44:58 +0000
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