# Investigation of Cavitation Noise in Cavitating Flows around an NACA0015 Hydrofoil
## 1 Introduction
The mutual interaction among a cluster of cavitation bubbles was also investigated. [PERSON] [12] analyzed the inner flow field of the axial pump to reveal the cavitation mechanism. The results showed that cavitation performance is enhanced by positive inlet guide vane angles but hampered by negative ones. So many works have focused on cavitation evolution in recent years, but little attention has been paid to cavitation noise. Cavitation-induced noise is an essential issue to be solved. Some research about different hydraulic machinery has been proposed. [PERSON] and [PERSON] [13] experimentally measured the noise for a three-dimensional hydrofoil at different attack angles. [PERSON] [14] investigated the relationship between the cavitation patterns and flow-induced noise for a model propeller through experiments. [PERSON] [15] conducted an experiment in a contraction-divergence channel to investigate the bubble pattern and cavitation noise under different liquid speeds. Numerical approaches have also been applied to investigate cavitation noise. [PERSON] [16] focused on an acoustic analogy based on a classical theory of Fitzpatrik a Strasberg to verify the direct simulation and analyze the source of noise. [PERSON] [17] investigated the effects of cavitation-flow patterns of hydrofoils, with an emphasis on turbulence models, and corresponding radiated noise was analyzed. [PERSON] [18] transformed bubble volume pulse to propeller cavitation noise using the Lighthill equation. Previous investigations on cavitation focused mainly on engineering applications, such as cavitation noise in hydro turbine and pump, but the mechanism has not been reflected and its control measures are mainly based on engineering experiences. Also, cavitation is an intricate phenomenon. With changes in boundary conditions, the morphology and patterns of cavitating vary a lot. Thus, the characteristics of noise radiated by cavitating flow are complex. Previous studies on cavitation noise are limited, and the mechanism and acoustic characteristics of different cavitation numbers have not been fully investigated. What is more, the cavitation number in different hydraulic engineering situations changes a lot. To be specific, the characteristics of noise induced by a quadrupole acoustic source, dipole acoustic source, and monopole acoustic source vary greatly with changes in cavitation numbers. To identify the source of noise and restrict the complex noise from different acoustic sources in various hydraulic engineering situations, a deeper understanding of the fundamental mechanism of cavitation-induced noise is essential. Thus, the present research focuses on this problem and figures out the mechanism and characteristics of cavitation-induced noise. The present study analyzes different acoustic characteristics of noise induced by the cavitation flow around an NACA0015 hydrofoil through numerical methods. Specifically, the numerical simulations are performed by the commercial software FLUENT. The filter-based turbulence model (FBM) and Zwart cavitation model were employed to calculate the flow field and accurately predict the cavitation phenomenon, while the acoustic analogy method based on the FW-H equation was applied to analyze the flow-induced noise with different cavitation numbers. Based on this research, the control measures can be improved to be more specific and effective.