Cavity induced vibration of flexible hydrofoils

• Published in: Journal of fluids and structures 2014-08, Vol.49, p.463-484
• Main Authors: Akcabay, Deniz Tolga, Chae, Eun Jung, Young, Yin Lu, Ducoin, Antoine, Astolfi, Jacques Andre
• Format: Article
• Language: English
• Subjects: Cavitation; Computational fluid dynamics; Engineering Sciences; Flexible; Fluid flow; Fluids mechanics; Frequency modulation; Hydrofoil; Lock-in; Mathematical models; Mechanics; Navier-Stokes equations; Structural mechanics; Turbulence; Turbulent flow; Vibration
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2014.05.007

The objective of this work is to investigate the influence of cavity-induced vibrations on the dynamic response and stability of a NACA66 hydrofoil at 8° angle of attack at Re=750000 via combined experimental measurements and numerical simulations. The rectangular, cantilevered hydrofoil is assumed to be rigid in the chordwise direction, while the spanwise bending and twisting deformations are represented using a two-degrees-of-freedom structural model. The multiphase flow is modeled with an incompressible, unsteady Reynolds Averaged Navier–Stokes solver with the k–ω Shear Stress Transport (SST) turbulence closure model, while the phase evolutions are modeled with a mass-transport equation based cavitation model. The numerical predictions are compared with experimental measurements across a range of cavitation numbers for a rigid and a flexible hydrofoil with the same undeformed geometries. The results showed that foil flexibility can lead to: (1) focusing – locking – of the frequency content of the vibrations to the nearest sub-harmonics of the foil׳s wetted natural frequencies, and (2) broadening of the frequency content of the vibrations in the unstable cavitation regime, where amplifications are observed in the sub-harmonics of the foil natural frequencies. Cavitation was also observed to cause frequency modulation, as the fluid density, and hence fluid induced (inertial, damping, and disturbing) forces fluctuated with unsteady cavitation. •We examine the influence of cavitating flows and flexible hydrofoils.•Cavitating flows excite the wetted natural frequencies.•Cavitating flows cause fluctuations in added-mass and frequency modulation.•Cavity shedding and sub-harmonics of the wetted natural frequencies may lock-in.•This is a combined numerical and experimental study.