Hydrodynamic Performance of Efficiency Transition Point of Forked Caudal Fins

Abstract

Thunniform fish has high swimming speed and swimming efficiency and thus becomes the ideal biological prototype of bionic robotic fish. In order to study the hydrodynamic characteristics of the efficiency transition point of the forked caudal fins of thunniform fish, the source terms influencing thrust and power consumption were mainly analyzed. The caudal fin model used the same surface area, aspect ratio, and fork length. To unify the metrics about the fin shape, the sweep angle was used to represent the structure for the forked caudal fins in this paper. It is found that the increase in the sweep angle attenuates the available area of the caudal fin of the thunniform fish, resulting in a lower reaction force to push the fluid downstream when the caudal fin swings. As a result, the thrust of the caudal fin decreases. Additionally, the rise in the sweep angle also triggers the enhancement of the strength and the development of the leading-edge vortex, thereby inducing greater vortex-augmented thrusts. However, an excessive increase in the sweep angle may trigger a decline in the thrust and efficiency, especially for a high Strouhal number, along with a decrease in power consumption. It is found that the sweep angle has an opposite action on the added mass force and vortex-augmented thrust by analyzing the source term of thrust.

Keywords

• biomimetic robotic fish
• forked caudal fin
• hydrodynamic performance
• vortex