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Thursday, February 9, 2012

Streamlined Swimming Like A Shark

Based on research funded by the National Science Foundation and published in the Journal of Experimental Biology, Harvard student Johannes Oeffner and Professor George Lauder found that the surface of high-tech swimsuits is not the element that helps improve swimming speed.

But that is not to imply that the swimsuits enhance speed. "I’m convinced [the swimsuits] work, but it’s not because of the surface of the [Speedo Fastskin II] swimsuits.

What we have shown conclusively is that the surface properties themselves don’t do anything for propulsion
."

While the Speedo Fastskin II is an earlier generation of high-tech swimsuits, Professor Lauder explains, "There are all sorts of effects at work that aren’t due to the surface. Swimmers who wear these suits are squeezed into them extremely tightly, so they are very streamlined. They’re so tight they could actually change your circulation and increase the venous return to the body, and they are tailored to make it easier to maintain proper posture even when tired. I’m convinced they work, but it’s not because of the surface."

The professor compared the man-made swimsuits with actual shark skin. "What we found is that as the shark skin membrane moves, there is a separation of flow. The denticles create a low-pressure zone, called a leading-edge vortex, as the water moves over the skin. You can imagine this low-pressure area as sucking you forward. The denticles enhance this leading-edge vortex. So my hypothesis is that these structures that make up shark skin reduce drag, but I also believe them to be thrust-enhancing."

He added some interesting observations and comments on future research. "If you watch a shark swim, the head does not move very much, so it could be that the denticles on the head are mostly reducing drag, but those on the tail are enhancing thrust. But we don’t know what that balance may be. Ultimately, though, one of the key messages of this paper is that shark skin needs to be studied when they’re moving, which hadn’t been done before."

He tested the skin of mako and porbeagle sharks, the Speedo Fastskin II and a material with tiny grooves in the aircraft and sailing industries with particle image velocimetry that uses a laser to illuminate millions of reflective particles in the water. Using a high-speed camera that records at up to 1,000 frames per second, he observed how the particles move and see where and when vortices form.

Professor Lauder is also exploring how to make an artificial shark skin and then modify it by deleting every other denticle, making the denticles twice as large, or changing the spacing in order to see its effects.

Note: Download this research here.

Copyright © 2012 by Open Water Source

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