P3.62 Friday, Jan. 6 Vortex perturbation of fish hovering FLAMMANG, B.E.*; ALBEN, S.; LAUDER, G.V.; Harvard University; Georgia Institute of Technology; Harvard University email@example.com
The pectoral fins of most fishes are flexible and deformable and their overall shape changes during a fin beat. While whole pectoral fins have been the subject of locomotor studies, there are few data on the kinematics and flexibility of single fin rays during swimming. In addition, nothing is known about the effect of fluid perturbations on the kinematics of fin rays of fish during normal swimming. We examined the curvature of the longest pectoral fin ray (third from dorsal edge) during steady swimming, hovering behavior and during a vortex perturbation provided during the fin beat. It was observed that during normal hovering behavior, a wave of curvature passed from base to tip and then tip to base of the fin ray during the course of one fin beat. The maximum curvature of the fin ray during normal hovering was 0.29 cm-1 in the proximal half of the fin ray and 0.54 cm-1 in the distal half of the fin ray. Perturbation of bluegill sunfish was accomplished by shooting vortices at the pectoral fin during hovering behavior. Kinematic analysis showed that the pectoral fin rays yielded substantially to the force of the vortex at the point of impact (maximum curvature = 1.13 cm-1), but that the rest of the fin ray did not deform (maximum curvature = 0.24 cm-1). We have also simulated the fin-vortex interaction using a computational fluid model which represents a 2D cross section of the fin and vortex ring. In the model, the fin is mainly repulsed by the vortex, but the distal edge curls towards it during the interaction. Comparison of the vortex impact on a fish fin with that of the model simulation suggests that structural properties of the fish fin ray may inherently dampen the effects of fluid perturbations.