Meeting Abstract

39.4  Monday, Jan. 5  Exceptional force generation is behind dolphins swimming prowess FISH, Frank E*; LEGAC, Paul; WILLIAMS, Terrie M; WEI, Tim; West Chester Univ.; Rensselaer Polytechnic Institute ; Univ. of California, Santa Cruz; Rensselaer Polytechnic Institute ffish@wcupa.edu

It has been a longstanding impression both within as well as outside of the scientific community that dolphins are effortless swimmers. This assertion has been promoted by what has been called Grays Paradox, where dolphins are not supposed to be able to swim fast with the available muscle mass, without the benefit of special drag reducing mechanisms. Previous uses of computational hydrodynamic models and gliding experiments have indicated that dolphins can produce high thrust (=drag), but these tests have relied on various assumptions. The thrust produced by two actively swimming bottlenose dolphins (Tursiops truncatus) was directly measured using Digital Particle Image Velocimetry (DPIV). For dolphins swimming in a large outdoor pool, the DPIV method used illuminated microbubbles that were generated in a narrow sheet from a finely porous hose and a compressed air source. The movement of the bubbles was tracked with a high-speed video camera. Dolphins were trained to swim steadily at 0.7 to 3.4 m/s or by fast starts within the bubble sheet oriented along the dorso-ventral midline of the animal. The wake of the dolphin was visualized as the microbubbles were displaced due to the action of the propulsive flukes and jet flow. The oscillations of the dolphin flukes were shown to generate strong vortices in the wake. Thrust production was measured from the vortex strength through the Kutta-Joukowski theorem of aerodynamics. The dolphins generated up to 425 N during steady swimming and up to 1468 N during fast starts. The results of this study demonstrated that dolphins produce more than enough thrust to propel themselves without reliance on special drag reduction mechanisms.