Meeting Abstract
The pectoral and pelvic appendages of the California sea lion (Zalophus californianus), like other pinnipeds, have been modified as flippers for movement in water. Unlike the foreflippers, which have a wing-like appearance and oscillatory movement for propulsion, the hindflippers are not used for thrust production in water, although the hindflippers are involved in terrestrial locomotion. The hindflippers are used as control surfaces for maneuvering underwater. When the digits of the flipper are abducted (spread), the hindflipper has a triangular planform. This design is similar to a highly swept delta wing. In addition, fleshy extensions of the digits provide a crenelated trailing edge to the flipper. To investigate its hydrodynamics, a hindflipper was spread and CT scanned to determine the three-dimensional geometry. Based on the CT scans, three models were printed: unmodified with crenelations, crenelations cut, and crenelations filled in. The lift and drag forces for each model was determined from flow tank testing at 1.0 and 1.5 m/s for angles of attack ranging from -25 to +25 deg. The lift coefficients with respect to angle of attack were similar for the three models and like delta wings they did not stall at highest angles of attack tested. The crenelated flipper had the higher maximum Lift/Drag ratios at higher positive and negative angles of attack compared to the modified flippers. The design of the hindflippers in sea lions as a delta wing with a crenelated trailing edge is useful for sea lions as a passive control surface at high angles of attack to execute sharp turning maneuvers.
