Meeting Abstract

S11.7  Wednesday, Jan. 6  Separating the effects of swimming mode and body shape in undulatory swimming TYTELL, E.D.**; BORAZJANI, I.; LAUDER, G.V.; SOTIROPOULOS, F.; University of Maryland, College Park; St. Anthony Falls Laboratory, University of Minnesota; Harvard University; St. Anthony Falls Laboratory, University of Minnesota tytell@umd.edu

Fish body shape and swimming mode are generally correlated. Slender-bodied fishes such as eels, lampreys, and many sharks tend to swim in the anguilliform mode, in which most of the body undulates at high amplitude. Fishes with broad tails and a narrow caudal peduncle, in contrast, tend to swim in the carangiform mode, in which only the tail undulates at high amplitude. Such fishes also tend to have different wake structures. Carangiform swimmers generally produce two staggered vortices per tail beat and a strong downstream jet, while anguilliform swimmers produce two pairs of vortices per tail beat and relatively little downstream flow. Are these differences a result of the swimming modes or the body shapes, or both? We present experimental results from a robotic flapping fin, along with data from swimming eels (anguilliform), bluegill sunfish (carangiform), and rainbow trout (subcarangiform), which indicate that the kinematic differences are small, and show strongly three-dimensional flow. Mackerel and lamprey swimming was also simulated computationally with realistic body shapes and both swimming modes: the normal carangiform mackerel and anguilliform lamprey, then an anguilliform mackerel and carangiform lamprey. Both experimental and computational results indicate that anguilliform swimmers are more efficient at lower swimming speeds, while carangiform swimmers are more efficient at high speed. Simulated wakes depended strongly on Strouhal number, but were largely unaffected by body shape or swimming mode. The differences between computational and experimental results may lie in a subtle interaction of Strouhal and Reynolds number, and potentially in the effect of body flexibility.