Revealing partial and simultaneous double lock-in phenomena in composite hydrofoils: Effects of bending-twist coupling

Adaptive composites are widely employed in various hydraulic and marine applications, such as propulsors, turbines, and renewable energy-harvesting devices. This study investigates vortex-induced vibrations (VIV) in carbon fiber-reinforced plastic (CFRP) hydrofoils with different ply angles, focusing on the lock-in phenomenon. A multi-field synchronous measurement system was developed to simultaneously capture vortex dynamics and structural vibrations. The vibration spectrum under various flow velocities revealed distinct lock-in behaviors for the CFRP hydrofoils with different ply angles. The hydrofoil with 45° ply angle exhibited a “partial lock-in” behavior, characterized by dual lock-in peaks during secondary frequency lock-in. In contrast, the hydrofoil with −45° ply angle displayed a “double lock-in” phenomenon, marked by the simultaneous occurrence of two lock-in events. To elucidate the underlying mechanism, dynamic mode decomposition (DMD) was applied to identify the dominant vortex structures and their frequency characteristics in the wake during “partial lock-in”. This work provides methodological insights and engineering paradigms for the vibration suppression design of next-generation high-performance composite hydraulic equipment.