Suppressing tip vortex cavitation through passive deformation of a hydrofoil. I. Bending

Tip vortex cavitation (TVC) remains a persistent issue in marine propulsion and lifting surfaces, contributing to the underwater radiated noise of marine vessels. We investigate a novel passive strategy for TVC mitigation through localized chord-normal bending of an elliptical NACA (National Advisory Committee for Aeronautics) 66(2)-415 hydrofoil. The hydrofoil is geometrically modified using modal deflection shapes characterized by spanwise bending length and deflection angle on the suction or pressure side. High-fidelity large eddy simulations of cavitating multiphase flow in various bending configurations are performed using our recently developed variational cavitation flow solver. These bending configurations involve full-, half-, and quarter-span bending by bending angles within the range of −20° to 30°. The effect of these parameters on the core pressure of the tip vortex, the cavitation volume, and the hydrodynamic performance is assessed. The results demonstrate that chord-normal bending, both toward the suction and pressure sides, can weaken the tip vortex flow and suppress TVC with pressure-side bending leading to superior TVC mitigation. Examining the hydrodynamic performance of the hydrofoil in various bending configurations reveals that pressure-side bending leads to reduced drag and improved lift, resulting in an improved lift-to-drag ratio compared to the baseline hydrofoil. However, a minor reduction in lift and an increase in drag are observed in the case of suction-side bending. Quantitative comparisons using a newly introduced integrated performance index (IPI) reveal optimal tradeoffs between cavitation suppression and lift-to-drag performance. Among the various bending configurations studied in this work, the highest IPI is observed in the HS−N20 (half-span bending by −20°) case, in which the tip vortex cavity volume is decreased by 99.5% at σ=1.4 compared to the plain hydrofoil, and an improvement by 9.9% is achieved in the lift-to-drag ratio. Through a detailed analysis of the tip vortex circulation, wake behavior, and boundary layer flow, we show that pressure-side bending weakens the rolled-up circulation via reduced spanwise advection of wake vorticity. In contrast, suction-side bending delays vortex formation by limiting the initial spanwise boundary layer flux near the tip. These findings establish chord-normal bending as a promising passive design paradigm for cavitation control in marine propulsors and lifting surfaces.