Hydrodynamic interactions between high-frequency pitching propulsors

High-performance swimmers such as tuna often operate at high frequencies, yet experimental studies of pitching hydrofoils are often conducted at low frequencies. What results is a gap between the complex biological system and its low-order representation. In this experimental study, we use high-frequency pitching hydrofoils to achieve high Reynolds numbers while maintaining biologically relevant Strouhal numbers. We investigate the hydrodynamic interactions between high-frequency pitching propulsors and show that these interactions are dictated by the kinematics and spacing of neighboring swimmers. We find that equilibrium constellations of the schooling swimmers can be manipulated by changing the pitching frequency. We use multi-layer stereo PIV to capture three-dimensional flow structures within these constellations to further understand their formation mechanism. Understanding the schooling mechanism at high frequencies can provide insights into the design and control of future high-speed multi-agent bio-inspired robotic platforms.