 (Stock photo/Mark Interrante) With the aid of a digital flow-tracking technology, fluid dynamicist Timothy Wei and his colleagues have, for the first time, directly addressed Gray's paradox--and proven it wrong. (This file is licensed under Creative Commons Attribution ShareAlike 2.0 License.)
Dolphin Swimming Mystery Solved with Imaging Technology
American Physical Society
NOVEMBER 21, 2008 From dolphins to clams to flying creatures like hummingbirds and bats, many of nature's most fascinating creatures exhibit forms of fluid flow. When the 61st Annual Meeting of the American Physical Society (APS) Division of Fluid Dynamics takes place from November 23-25 at the San Antonio Convention Center, researchers from across the globe will describe cutting-edge research with applications in astronomy, engineering, alternative energy, biology, and medicine.
Several highlights from the more than 1,500 presentations at the meeting are listed below.
HIGHLIGHTS OF THE MEETING
1) Wind-Tunnel Studies Reveal Bat Flapping Secrets
2) Robotic Hummingbird Offers Insight into Hovering Flight
3) Dolphin Swimming Mystery Solved with Digital Imaging Technique
4) Engineers Unearth the Digging Secrets of Burrowing Clams
5) Are Flexible, Flapping Flying Machines in Our Future?
6) Modeling Embryonic Heart Development
7) Walkers' Wakes can Spread Germs in Airplanes
3) DOLPHIN SWIMMING MYSTERY SOLVED WITH DIGITAL IMAGING TECHNIQUE
Since the 1930s, scientists have puzzled over the high speeds at which dolphins swim. Dolphins were not thought to be capable of generating enough thrust to overcome the drag they would experience at high speeds from the turbulent flow of water around their bodies--a conundrum known as Gray's paradox (after biologist Sir James Gray, who first noted it). That led biologists to speculate that dolphin skin must have unusual turbulence-reducing properties which let them swim fast.
Now, with the aid of a digital flow-tracking technology, fluid dynamicist Timothy Wei and his colleagues have, for the first time, directly addressed Gray's paradox--and proven it wrong.
Wei, a professor at Rensselaer Polytechnic University in New York, and his colleagues used Digital Particle Image Velocimetry (DPIV). In the technique, the fluid flow within a digital camera's field of view is determined by charting the movement of small particles distributed throughout the fluid. In experiments conducted at the Long Marine Laboratory at the University of California, Santa Cruz, the scientists measured the flows produced by two dolphins doing tailstands--a Sea World-worthy maneuver in which dolphins hold themselves vertically out of the water, using quick, strong oscillations of their tail. The data revealed that special skin wasn't necessary, because thrust produced by the dolphins' tails was "far more than necessary to overcome turbulent boundary layer drag," says Wei, who plans to use the DPIV technique to measure flow around other marine mammals. "These measurements create greater opportunities for addressing interesting and long-standing questions about swimming," he says.
Wei's talk, "DPIV measurements of dolphins performing tailstands," is at 8:13 am on Monday, November 24, 2008, in Room 102A of the San Antonio Convention Center. Abstract: http://meetings.aps.org/Meeting/DFD08/Event/90214.
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