Study on the Hydrodynamics of Manta-Like Robots Varying Span-Section when Flapping Asymmetrically

Manta rays have attracted extensive attention from bionic scholars due to their beautiful streamlined shape, flexible maneuvers and efficient propulsion mechanism. When swimming, manta rays will show asymmetric characteristics in time and space during the up and down beats. A deep understanding of the hydrodynamic characteristics of manta rays during movement will help the development of bionic underwater submersibles. This paper builds a hydrodynamic experimental platform for manta ray flexible pectoral fins to conduct bionic propulsion experiments, exploring the hydrodynamic characteristics when the manta ray asymmetric motion parameters are changed. The chord-wise section of the bionic pectoral fin in this paper is designed using the NACA foil series. Considering that the flexibility of the manta ray pectoral fin obtained by NACA foils of different thicknesses is different, this paper also studied the changes in hydrodynamic characteristics when the pectoral fin section airfoil is changed. Results show that when beating asymmetrically, there is a small impact on thrust while a large impact on lift. When the foil of the pectoral fin gets thicker, asymmetric flapping can improve propulsion efficiency. When flapping with asymmetric frequency, the upstroke will change significantly with the change of frequency. Appropriate asymmetric flapping of fast up and slow down can obtain better hydrodynamic characteristics.