Unsteady Cavity Induced Vibrations of Flexible Hydrofoils

The objective of this study is to investigate the dynamic interplay between elastic foil deformation and unsteady sheet/cloud cavitation. Recently, there is increasing interest in the use of light and flexible materials in marine propulsion devices and controlled surfaces, which can deform/vibrate due to un-intentional overload when operating in off-design conditions, or due to intentional passive/active controlled response of the hydrofoil. Numerical studies are conducted by applying a new hybrid coupling approach to efficiently and stably couple a URANS solver with a simplified structural model of the cantilevered, rectangular foil represented by a two degree-of-freedom system. The numerical model is first validated with experimental measurements of a rigid and a plastic NACA 66 hydrofoil. Next, numerical results are shown for plastic NACA 66 hydrofoil with varying mass and stiffness in turbulent subcavitating and cavitating flows. The influence of varying mass and stiffness on the cavitation patterns, vorticity contours and flow streamlines, bending and twisting deformation, and hydrodynamic load coefficients are presented. In particular, results are shown for un-locked and locked-in response due to unsteady sheet/cloud cavitation induced vibration.