FISH, F.E.; KETTEN, D.R.; West Chester Univ., PA; Woods Hole Oceanographic Institution: Examination of three-dimensional geometry of cetacean flukes using CT-scans

The flukes of cetaceans function in the hydrodynamic generation of forces for thrust, stability, and maneuverability. The three-dimensional geometry of flukes is associated with the production of lift and drag. Previous studies of fluke geometry have been limited in the number of species examined and the resolution of measurements. Data on fluke geometry were collected from seven odontocete cetaceans. Flukes were imaged as 1 mm thickness cross-sections using X-ray computer-assisted tomography (CT-scanning) and digitally reassembled to determine the three-dimensional geometry. Fluke shapes were characterized quantitatively by dimensions of the chord, maximum thickness, and position of maximum thickness from the leading edge. Sections had a blunt, rounded leading edge and a highly tapered trailing edge. At 50% of span, the thickness ratio (maximum thickness/chord) among species was generally uniform, ranging from 0.19 to 0.24. These low values would indicate reduced drag while moving at high speed. The flukes of Globicephala (pilot whale) and Tursiops (bottlenose dolphin) had the position of maximum thickness from the leading edge located at 0.30 chord, whereas the maximum thickness for Phocoena (harbor porpoise) was at 0.24 chord. The more posterior displacement of the maximum thickness reduces the tendency of the boundary flow to separate, potentially affecting drag and stall patterns. Variation in the structure of cetacean flukes reflects different hydrodynamic characteristics that could influence swimming performance.