The Impact of Dorsal Fin Design on the Swimming Performance of a Snake-Like Robot

Lampreys’ posterior dual dorsal fins can function as a thrust booster. In addition, the fin-fin interaction of these dorsal fins enables utilization of the energy from the wake, making this species one of the most efficient swimmers. Thus, this dorsal fin configuration can serve as a great source of inspiration for improving the swimming speed and efficiency of bioinspired underwater robots. We perform a systematic experimental and computational study to understand the impact of a dual dorsal fin design on swimming speed and efficiency of an underwater snake-like robot. In the proposed dorsal fin structure, the hind fin often operates in the wake of the fore fin. Hence, its performance is affected by the vortices shed by the fore fin. The spacing of the two dorsal fins and the robot’s oscillation parameters significantly impact the swimming performance of the snake-like robot. Four different spacings ranging from 0 to 3 link gaps were tested at three different amplitudes ( $15^\circ$ , $30^{\circ }$ and $45^{\circ }$ ) and angular velocities (2, 3 and 4 rad/s). It was found that changes in the spacing and kinematic parameters would significantly affect the interactions of the vortices shed from the fore and hind fins. This interaction, in turn, affects the vortex formation on the hind fin, resulting in changes in wake strength and formation direction, which would significantly affect the swimming speed and efficiency of the underwater snake-like robot. These findings provide better understanding of how dual dorsal fins and the respective fin-fin interactions affect the swimming performance and can be used as guidelines for designing bioinspired underwater robots.