Fluid and Structure Coupling Analysis on Frequency Locking of an Elastic Hydrofoil

Vortex-induced vibration (VIV) has always been a significant research topic in relation to marine structures, with structural resonance and locking vibrations liable to occur at particular Reynolds numbers. To investigate this problem, fluid-structure coupling simulations of an elastic hydrofoil within a viscous flow are conducted. The correlation between the structural response and vortex shedding was explored. By analyzing the frequency eigenvalues, the structural response and vortex shedding at different frequencies can be decoupled. The findings suggest that the self-sustainability of natural vibration plays a significant role in frequency lock-in once structural resonance has been triggered. The phase difference between the lift pulsation and vortex shedding is determined, and is confirmed to be a significant factor influencing the resonant vibration of elastic foils. This phase difference can be used to determine whether the lock-in phenomenon has occurred. It is also found that veering phase, the resonance appears as forced vibration, while at locking phase, the resonance appears as self-sustained vibration at a natural frequency.