Investigation of Lock-in Characteristics of Flexible Cantilevered Hydrofoils

We numerically study the coupled vortex-cavity dynamics in a flexible cantilevered NACA66 hydrofoil at a Reynolds number of 7.5x10⁵. The fluid-structure interaction of this system is of interest in characterizing the cavitation-induced noise and vibration of marine propellers. Flexible cantilevered hydrofoils have been found to exhibit lock-in characteristics in the cloud cavitation regime (0.5 ≤σ ≤1.4). Through numerical simulations, we investigate the mechanisms leading to the onset of lock-in, specifically the emergence of bend-twist coupling, the dynamics of re-entrant jet and vortex-cavity interactions within the lock-in regime. As part of the study, we identify the coherent structures driving the dynamics of the cloud-cavitation through spectral proper-orthogonal decomposition of the flow field properties. The present investigations provide spatio-temporal insights into the underlying cavity breakdown and vorticity transport mechanisms (baroclinic torque, advection, diffusion), which influence the performance of marine propellers. Based on these investigations in the cloud-cavitating lock-in regime, design strategies can be developed to mitigate the adverse effects of vibration and noise arising in marine propellers.