Flapping strategies for high-maneuverability pitching in the cownose ray

Most previous studies on ray swimming focus on hydrodynamic characteristics of separate single fins while neglecting multi-fin vortex coupling, and few studies quantify the combined pitching control effects of coordinated asymmetric pectoral flapping and caudal fin deflection. To fill this research gap, this paper uses three-degree-of-freedom (3-DoF) self-propelled simulations relying on an in-house fluid solver to investigate the high-maneuver pitching hydrodynamics of cownose rays. Results show that increasing the caudal fin deflection angle (α) improves pitching agility with a thrust penalty. At α = ±40°, caudal vortex shedding displaces pectoral trailing-edge vortices, and the synergistic vortex interaction produces large pitching moments for rapid attitude adjustment. Due to the asymmetric body morphology of rays, α = 20° contributes to stable swimming, and downward deflection achieves better pitching performance than upward deflection. The heave amplitude ratio (HAR) also determines the vertical pitching direction of rays. HAR = 3.00 generates upward pitching with large-scale leading-edge vortices (LEVs), whereas lower HAR leads to downward pitching with suppressed LEVs. The coordination of dual-fin kinematics realizes somersault locomotion, with forward somersaults possessing superior agility and faster response than backward somersaults. These findings reveal that synergistic fin kinematics and multi-fin coupling strategies allow rays to achieve rapid, highly maneuverable pitching and somersaulting and provide reliable theoretical support for the design of high-agility bionic underwater vehicles.