Meeting Abstract

58.5  Thursday, Jan. 5  Exploring the parameter space for Kármán gaiting: kinematics across speed and size LIAO, James C.*; TAGUCHI, Masashige; Whitney Lab, Univ. of Florida, Gainesville; Whitney Lab, Univ. of Florida, Gainesville jliao@whitney.ufl.edu

Very little is known about how swimming fish relate to turbulence. We measured the body kinematics of 12.1 ± 0.4 cm (mean ± standard error) rainbow trout (Oncorhynchus mykiss) Kármán gaiting in a vortex street behind a 5 cm D-section cylinder (n=6 fish). We increased the flow velocity from 2.5 -11 body lengths per second (L s ^-1 ) and found that tailbeat frequency shows a u-shaped curve. Lateral body amplitudes and body wavelength exhibited a reverse u-shaped curve, plateauing at the highest flows. Head angle remained relatively constant until the highest flow velocities. Maximum body curvature was the only variable that increased in a linear fashion with speed, while its position on the body was the only variable that did not show a pattern across speed. Body wavelength and its propagation down the trunk increases with swimming speed, but wavelength decreases at the highest speed. We next ran the same experiment with fish of different body lengths (8.5-18.1 cm, n= 5 fish). At the highest speeds, smaller fish had a lower tailbeat frequency than larger fish, whereas at slow speeds tailbeat frequency was similar for all fish. Lateral body amplitudes, once normalized to body size, were similar across fish sizes. The exception was for the center of mass, which heaved substantially less for a larger fish. Larger fish had a longer body wavelength than smaller fish. Smaller fish had a larger maximum body curvature, the location of which moved rostrally with increasing swimming velocity, but more slowly than compared to larger fish. Smaller fish also possessed larger maximum head angles. Our results reveal new patterns in Kármán gait kinematics that shed light on how flow speed and body length can facilitate or constrain vortex capture.