Hydrodynamic performance and pursuit mechanisms of dual self-propelling fish in different queue modes

In this study, a computational fluid dynamics model is employed to investigate the influence of different flocking behaviors on the hydrodynamic performance of dual-fish propulsion systems. The primary objective is to understand how the varying initial spacing affects propulsion efficiency and group dynamics. The results indicate that a compact arrangement enhances the thrust and efficiency owing to hydrodynamic interference, with a maximum thrust improvement of 42% and an efficiency gain of 13% when fish are in tandem. However, excessively small spacing can reduce speed and displacement. Optimal conditions occur when the longitudinal spacing (Gx/L ≥ 1.0) and lateral spacing (Gy/L ≤ 0.5) are maintained, resulting in a 7% increase in speed and displacement. This study identifies three pursuit mechanisms based on displacement variations, highlighting a periodic “saturation” phenomenon where fish maintain a stable parallel formation. Furthermore, the pursuit mechanism between the two fish is categorized into three types. In mechanism I, the displacement of fish #1 decreases, whereas that of fish #2 increases. Both fish experience reduced displacement in mechanism II and they exhibit increased displacement in mechanism III. These findings suggest that adjusting the interspacing in biomimetic propulsor clusters can enhance the group propulsion efficiency and stability, providing insight into underwater behavioral control and biomimetic engineering applications.