Hydrofoil sound generation at high Reynolds number

Abstract

The unsteady separated turbulent flow near the trailing edge of a loaded hydrofoil is often a source of hydroacoustic noise. Intense turbulence in this region may produce noise directly, but, at low Mach number, hydrodynamically forced structural motions may also radiate sound. In fact, interactions between the foil’s unsteady vortical wake flow and the hydrofoil structure may produce undesired self-excited hydrodynamic-vibratory resonances sometimes called ‘‘singing.’’ This presentation reports experimental results from a series of recent experiments focused on understanding and documenting these phenomena at chord-based Reynolds numbers up to 60 million. The measurements include foil surface static and dynamic pressures, foil vibration, LDV-determined average flow velocities and turbulence quantities, and PIV flow fields in the immediate vicinity of the foil’s trailing edge. The experiments are conducted at the US Navy’s Large Cavitation Channel with a two-dimensional test-section-spanning hydrofoil (2.1 m chord, 3.0 m span) at flow speeds from 0.5–18.3 m/s. Special interest is focused on the trailing edge of the foil where the unsteady Kutta condition is investigated. [Significant assistance provided by personnel from NWSC-CD. Sponsored by Code 333 of ONR.]