The motion of self-propelled flexible structures in Kármán vortex streets (a common natural/engineering flow field) is critical for underwater biomimetic robots and medical microcarriers. However, current gaps exist: limited research on self-propelled filaments, unclear coupled effects of flutter parameters hindering application development. In this study, the kinematic characteristics of self-propelled flexible filaments in Kármán vortices are investigated via numerical simulations with the immersed boundary method. The analysis focuses on how the flutter parameters, the Reynolds number (Re), and the Strouhal number (StA) influence the filament movement state and the drag coefficient. The results indicate that the motion of the filament is significantly affected by its initial position, Re, and flutter amplitude. At lower Re values (100), the filament advances steadily across all StA values. In contrast, higher Re values (150, 200, and 250) yield complex motion patterns, including both advancing and retreating behaviors. Notably, within the StA range of 0.2–0.4, which corresponds to the optimal propulsion efficiency observed in fish, the filament shuttles between different vortex cores. This behavior mirrors fish propulsion mechanisms, highlighting energy-efficient movement. These findings provide insights into the hydrodynamic mechanisms of self-propelled flexible filaments, which are crucial for designing underwater propellers and medical microbionic robots. By laying a theoretical foundation for broader applications like microfluidic mixing devices and low-energy-consumption underwater explorers, we drive progress in both fluid mechanics theory and interdisciplinary engineering innovation.
Yu et al. (Sun,) studied this question.