Hydrodynamic Characteristics and Transient Flow Field Analysis of a Manta Ray-inspired Robot in Steady Inflow

The complex marine environment poses significant challenges for the efficient and stable propulsion of underwater robots. The manta ray, with its high propulsion efficiency and superior maneuverability derived from the Median Paired Fin (MPF) propulsion mode, provides an excellent bionic prototype for underwater robot design. This paper focuses on a manta ray-inspired robot, employing Computational Fluid Dynamics (CFD) to numerically simulate its cruising process under a steady inflow of 0.1 m/s with sinusoidal pectoral fin flapping. A detailed analysis of its hydrodynamic characteristics and transient flow field structure is conducted. The results indicate that the mean drag force on the robot is 0.36N, with a dominant frequency in its energy spectrum of 0.5Hz. The lift force exhibits large-amplitude periodic oscillations, with a primary frequency of 1.0Hz accompanied by higher harmonics. Visualization of the static pressure and velocity fields over a complete motion cycle reveals that the flapping of the pectoral fins induces alternating high- and low-pressure zones on either side. The evolution of the flow field visually confirms that thrust is generated by the reverse jet flow excited by the fin flapping and the resulting pressure differential. This study elucidates the propulsion mechanism of the manta ray-inspired robot's pectoral fin flapping from the perspective of the transient flow field, providing a theoretical basis for its subsequent hydrodynamic optimization and intelligent control.