Effects of asymmetrical pectoral fins’ flapping on the turning performance of a cownose ray

Cownose rays have agile turning maneuverability for predator avoidance and obstacle evasion during self-propelled swimming, relying on left-right asymmetrical pectoral fins’ flapping in amplitude, frequency, and wavenumber. The asymmetrical flapping turning modes are calculated by using an in-house fluid solver. In the single-sided flapping mode, the turning radius remains small, but a pronounced “pre-displacement” occurs in the trajectory, and the maneuver requires a relatively long duration. With decreasing amplitude difference between the left and right fins, the turning radius gradually increases, while the turning time is reduced. In asymmetrical frequency modes, low-frequency flapping on one side reduces turning time and enhances maneuverability, with an optimal frequency further boosting efficiency. Among asymmetrical wavenumber flapping modes, the optimal flapping wavenumber for efficient locomotion is determined by co-directional asymmetrical flapping. Conversely, the left-right reversed wavenumbers flapping exhibits the fastest rotational response and the largest turning angle compared to other turning modes, while facilitating high-performance in-place turning. This work systematically investigates and reveals the turning characteristics of cownose rays under different asymmetrical flapping strategies, thereby providing insights into understanding the turning locomotion mechanisms of cownose rays.