FISH, F.E.*; NUSBAUM, M.K.; BENESKI, J.T.; KETTEN, D.R.; WILLIAMS, T.M.; West Chester University; West Chester University; West Chester University; Woods Hole Oceanographic Institution; Univ. of California, Santa Cruz: Dolphin flukes as passively self-adjusting flexible propulsors
The flukes are the main locomotor structure in cetaceans. Effective thrust generation is a function of the fluke kinematics, angle of attack, and fluke shape. We investigated the effect of bending within the caudal region of odontocete cetaceans to determine how changes in angular displacement between caudal vertebrae could effect passive shape change of the flukes. Lateral and posterior views from high-speed video of Tursiops truncatus freely swimming and statically pushing against a load cell showed substantial chordwise and spanwise fluke flexibility. Spanwise bending was restricted to the fluke tips. Fluke chord was maximally bent as the fluke changed vertical direction during the oscillatory cycle with a chord reduction of 31.6-35.1%. Internal and external changes of bent flukes were examined with CT scans. Flukes and tailstock were removed from deceased Delphinus delphis, Lagenorhynchus acutus, Phocena phocena, Peponocephala electra, and Tursiops truncatus, and bent on an adjustable support at 0, 45, and 90,o. At 0o, flukes displayed symmetrical cross-sections. Cross-sections of bent flukes (45o, 90o) were asymmetrical and showed a cambered profile. Maximum cambering occurred close to the tailstock and decreased toward the fluke tip. Maximum angular displacement occurred at the �ball vertebra�, located posterior of the anterior insertion of the flukes on the tailstock. Bending at the �ball vertebra� passively cambers the flexible flukes. Cambering could increase thrust generation during swimming, particularly during direction reversal in the oscillatory cycle. In addition, bending at the fluke tips would act like winglets to control tip vortices, enhancing thrust production and hydrodynamic efficiency.
