Meeting Abstract

P1.90  Friday, Jan. 4  The hydrodynamics of ground effect in relation to the head shape of the spotted eagle ray GABLER, M K*; FISH, F E; BENESKI, J T; MULVANY, S; MOORED, K W; West Chester Univ., Pennsylvania; West Chester Univ., Pennsylvania; West Chester Univ., Pennsylvania; Univ. of South Florida, Tampa ; Princeton Univ. New Jersey mg731541@wcupa.edu

Eagle rays are epipelagic batoids that forage on the ocean bottom. Unlike other members of the family Myliobatidae (e.g., Rhinoptera, Manta) that possess paired cephalic lobes around the mouth, the eagle rays have a prominent flattened bill-like rostrum. CT scans of the head of a spotted eagle ray (Aetobatus narinari) were used to define the external geometry to produce a scale model of the ray head with a 3D printer (ZPrinter 450). The model was tested in a flow tank over a range of flow speeds from 0.06 to 0.43 m/s. A multi-axis force transducer was used to measure lift and drag of the model head in mid-water and in close proximity to the bottom at angles of attack from -10^o to 10^o. At 0^o angle of attack, a negative lift was generated by the model head when situated in the water column, but a slight positive lift was produced when the model was in close proximity to the bottom. Compared data from the model situated in the water column, the bottom produced a substantial ground effect which enhanced the lift production for both positive and negative angles of attack. The model head was modified with dye injection ports for flow visualization. The dye streams indicated that the rostrum acted like a delta wing. The delta shape makes wings less likely to stall and thus maintains lift production. When foraging, eagle rays swim with the head angled down in contact with the substrate. The increased negative lift from ground effect would aid in stabilizing the head to keep the sensory surface of the rostrum in contact with the substrate and counter any pitching motions induced by oscillations of the pectoral fins.