LES investigation of cavitation harmonic tone around a Delft twist-11 hydrofoil

Abstract

In this paper, a hybrid CHA approach, including the LES approach and the permeable Ffowcs Williams-Hawkings (PFW–H) equation, is adopted to predict the cavitating flow and its induced noise around a Delft Twist-11 hydrofoil. The predicted hydrodynamic result shows good agreement with the measured one. A simplified equation for pseudo-thickness noise is proposed, indicating a close relationship between pseudo-thickness noise and cavity volume fluctuation. With this simplified equation, the characteristic of pseudo-thickness noise and its connection with cavitation evolution are discussed. The hydroacoustic result indicates that the cavitation noise around a twisted hydrofoil is mainly contributed by the pseudo-thickness term. Moreover, the harmonic characteristic of pseudo-thickness noise is observed, which is mainly controlled by the collapse of the separated cavity, the accelerated growth of the attached cavity, and the collapse of the primary U-shaped cavity. Finally, with the assistance of wavelet transform and bispectrum analysis, the inducement of tone at 1st harmonic is attributed to the collapse of the primary U-shaped cavity, which can simultaneously raise a significant interaction coupling of tones at low-order harmonics to strengthen the tones at high-order harmonics. Our work reveals the relationship between cavitation harmonic tones and cavitation structure, which is helpful for the understanding of hydroacoustic mechanism.