Kinematic and hydrodynamic mechanisms of Misgurnus anguillicaudatus during routine turning

Although traditional underwater thrusters are technologically advanced and widely used, they have limitations in propulsion efficiency, flexibility, and noise. Studying the swimming mechanisms of aquatic organisms can provide new insight into submarine propulsion. The kinematics and hydrodynamic mechanisms of Misgurnus anguillicaudatus in the turning process were explored experimentally through particle image velocimetry. Morphological characteristics of Misgurnus anguillicaudatus locomotion were analyzed using the swimming posture and extracted a body trunk curve. The kinematic characteristics of Misgurnus anguillicaudatus during turning maneuvers were further explored through quantified kinematic parameters. The hydrodynamic mechanism of the turning process was analyzed from the perspective of transient kinetic energy, vortex evolution, and pressure characteristics. The body trunk of Misgurnus anguillicaudatus maintained a fluctuating pattern from the beginning of the movement. Relying on periodic body undulations and periodic tail wagging enables the fish to maintain a continuous maneuvering state. The tail wagging in different directions generates a pair of positive and negative vortices and local high-kinetic-energy regions. The combination of pressure and viscous mechanisms creates vorticity. Jets are generated at the interface between converging vortices and opposite spins. The thrust jets provide thrust, and the side jets provide angular momentum to the fish body and the surrounding additional mass. The pull of the negative pressure area on the body along the trough is the main thrust mechanism that enables Misgurnus anguillicaudatus to swim.