Flow Structures Generated by Robotic Sea Lion Flippers of Varying Elasticity and Angular Velocity

The California sea lion produces thrust by clapping its foreflippers to its body, followed by a streamlined glide. This maneuver produces wake structures that are significantly different from those created by other biological swimmers that rely mostly on body/caudal fin (BCF) locomotion. Through the creation of a passively actuated sea lion foreflipper, we simulate the clapping motion against a plate to investigate the flow structures that result using particle image velocimetry (PIV). Previous research has examined the resulting flow structures of a singular flipper rotating at a constant angular velocity. It was found that suction side vortices in addition to the presence of two jets contribute to thrust production. The structures observed reveal similarities to those of impulsively starting flat plates. To expand on this and understand the effects of elasticity and angular velocity on the resulting flow structures, we investigate three flippers of different young’s modulus at constant angular velocities and altering angular velocity for each of the three flippers.