Group gliding of three manta rays in multiple formations

Abstract

Manta rays are often seen gliding and cruising in organized formations in oceanariums. We posed the following questions: (1) Why do they glide in a group? (2) What is the best group gliding formation? (3) How does the gliding attack angle affect the hydrodynamics of group gliding? To solve these questions, we first established a numerical model of the manta ray and then conducted numerical simulations of three manta rays engaged in tandem, orthotriangular, and antitriangular variable attack angle group gliding. The results show that group drag reduction can be produced in all three arrangements, and the critical attack angle of lift is −2°. In the tandem formation, the manta ray at the head of the group always experiences the least drag, and the lift of each individual is noticeably different. In the orthotriangular formation, the system drag reduction is more difficult to produce, and the lift of each individual is similar. In the antitriangular formation, system drag reduction can be produced at all attack angles due to the uniqueness of the flow field pressure distribution, and thus it is the most ideal group gliding formation.