An Experimental Analysis of the Structural Response of Flexible Lightweight Hydrofoils in Cavitating Flow

This paper presents an original experimental study concerning the structural response of a flexible lightweight hydrofoil undergoing various flow conditions including partial cavitating flow. It is based on the analysis of the static deformation, the vibrations, the strains, and the stresses of a polyacetal NACA0015 cantilevered hydrofoil in a hydrodynamic tunnel, at Reynolds numbers ranging from 3 × 10⁵ to 6 × 10⁵. A specific distance measurement laser device was developed to measure the static deformation of the hydrofoil. The vibration response was measured by means of two laser vibrometers in order to identify the structural modal response. The strains and stresses were obtained from integrated strain gauges embedded in the foil close to the root section. A high-speed camera was used in order to analyze unsteady features of the cavitating flow. This paper presents the experimental setup and several results in both noncavitating and cavitating flow that should be very useful for numerical developments of fluid structure interaction (FSI) in heavy fluid. Several observations are reported in the paper showing the strong coupling between the fluid and the structure. Particularly, a frequency lock-in of the cavity frequency to the first bending mode is clearly observed for a narrow band of cavitation numbers.