Numerical simulation of manta ray's self-propulsion

A manta ray is a typical representation of its pectoral fin propulsion mode, which is stable and conducive to wide area cruise, thus being suitable for bionic targets of a bionic vehicle. This paper established a computational model of the two-degree-of-freedom self-propulsion of the manta ray. Its motion equation and fluid dynamic equation were coupled to numerically simulate its self-propulsion process from stationary-state start-up and acceleration to steady-state cruise. The time history changes of the manta ray's swimming speed, hydrodynamic force, pressure distribution and three-dimensional flow field structure were analyzed. The simulation results show that, during the self-propulsion process of the manta ray, its speed, acceleration and displacement in its forward direction are completely determined by the net thrust generated during the flexible deformation of the pectoral fins and the net resistance encountered during its forward swimming. In the acceleration stage, the net thrust is superior and mainly generated near the tips of the pectoral fins. When the balance between the thrust and the resistance is reached, the manta ray is in its steady cruise stage. The flexible deformation of the spanwise and chordwise superposition of the pectoral fins may produce complex three-dimensional vortex structures. The numerical simulation method proposed in this paper and the study of the manta ray's self-propulsion process lay the foundation for further revealing its swimming mechanisms.