Meeting Abstract

33.5  Monday, Jan. 5  How ribbon-fin swimmers swim SHIRGAONKAR, Anup A; CURET, Oscar M; PATANKAR, Neelesh A; MACIVER, Malcolm A*; Northwestern University; Northwestern University; Northwestern University; Northwestern University maciver@northwestern.edu

What is the propulsion mechanism for fish with elongated ribbon-like fins, such as weakly electric gymnotiform fish, the African Gymnarchus niloticus, and others? We combine computational fluid dynamics and digital particle image velocimetry to uncover the principle of thrust generation for an idealized ribbon fin with sinusoidal deformation kinematics. We show that the primary mechanism of thrust production is the generation of a streamwise central jet and associated attached vortex rings. We derive scaling relationships for how thrust varies with various kinematic and structural parameters. We also show that in addition to surge force (parallel to the long axis of the fin), the fin can generate heave thrust (perpendicular to the long axis of the fin). The magnitude of the heave force increases with the ratio of the wavelength of the traveling wave along the fin to the length of the fin. For typical knifefish fin geometries, this crossover point is around 1.5. Thus the ribbon-fin confers the ability to generate thrust in multiple directions according to how many traveling waves the fish places on the fin. Our results will be useful for understanding the neural basis of control in the weakly electric knifefish and other aquatic animals that use similar propulsors, as well as for engineering bio-inspired vehicles with undulatory thrusters.