Experimental analysis of trailing edge hydroelastic coupling on a hydrofoil

Abstract

This paper explores the conditions for hydroelastic trailing edge vibrations generating tonal noise on a NACA0015 aluminium hydrofoil clamped in a hydrodynamic tunnel. Tests were performed for Reynolds numbers $Re$, ranging from $2\times 10^5$ up to $12\times 10^5$ and various angles of attack $\alpha$, from 0 up to 10°. A laser vibrometer was used to characterize the hydrofoil vibratory response. Time Resolved Particle Image Velocimetry (TR-PIV) was used to scrutinize the origin of the hydrodynamic excitation mechanism. Hydroelastic trailing edge vibrations of significant amplitude were observed at moderate angles of attack $4\le \alpha \le 8.5$°, for Reynolds number such that the pressure side boundary layer transition was located close to the trailing edge, with a frequency signature allowing a lock-in with the hydrofoil trailing edge structural mode. Two passive solutions were tested to mitigate this hydroelastic flow-induced vibration: a truncated hydrofoil and a triggered one. The truncated configuration slightly impacts the vibration while triggering the pressure side boundary layer transition ahead of the trailing edge eliminates the trailing edge vibrations with negligible impact on the hydrofoil hydrodynamics performances.