# Investigation of Cavitation Noise in Cavitating Flows around an NACA0015 Hydrofoil
## 1 Introduction  
Cavitation mainly occurs in the location where the local pressure of the liquid drops below the threshold value at a specified temperature. As the phenomenon occurs in a wide range of hydraulic engineering situations where liquid flowing systems are involved, cavitation sways numerous industries, such as petroleum transportation and the water pump industry. What is more, cavitation can generate destructive behavior. From previous experience, the effects of cavitation are various, such as causing pitting of the boundary surface and leading to vibration and noise problems. Therefore, fully investigating and understanding the mechanism of cavitation is essential for its widespread and undesirable features. In the last several decades, different experimental and numerical methods have been applied to the research of cavitation. Cavitation in various structures and characteristics has been studied by many investigators. Experimental studies generally observe the occurrence of a cavitation phenomenon and its hydrodynamic characteristics using a high-speed video camera. [PERSON] [1] observed the process of bubble occurrence, development, and collapse. This research elucidated the mechanism of bubble evolution of the high-speed centrifugal pump. There have also been some experimental observations around hydrofoils carried out by [PERSON] [2] in the cavitation tunnel to explain the spatial-temporal evolution of cloud cavitation. They found that U-type flow structures are common in cloud cavities,and sheet cavities always have a convex-concave profile. The shedding is generally caused by the converging re-entrant flows, which occur in the convex part, and the re-entrant flows are normal to the contour edge. [PERSON] [3] experimentally investigated the particle motions induced by bubble cavitation. They clearly recorded and analyzed the cavitation bubble dynamics and its induced particle moving dynamics. The results revealed that the distance between the particle and the cavitation bubble is an important influence factor in this phenomenon. [PERSON] [4] focused on the collapsing mechanism of a laser-induced cavitation bubble between a spherical particle and a solid wall. The influences of several paramount parameters were discussed in this paper. [PERSON] [5] used a high-speed camera to capture and observe the cavitation flow patterns in different stage. The study revealed the significant effect of different material on the cavitation flow. [PERSON] [6] experimentally analyzed the characteristics of the cavitation pattern and the vibration response around an NACA66 hydrofoil. Numerical approaches have also been presented and applied to efficiently investigate the cavitation phenomena. Among the most notable studies, [PERSON] [7] focused on the mechanism of the interaction between the fluid vortex production and cavitation. The analysis of the flow field showed that cavitation promotes vortex formation and increases the boundary layer thickness with the flow unsteadiness. [PERSON] [8] studied the turbulent vortex-cavitation interactions in transient sheet and cloud cavitation phenomena. Their analysis of the vorticity transport equation revealed a strong correlation between the cavity and vorticity structure. The interaction between the leading edge and trailing edge vortices was significantly changed by the transient development of sheet and cloud cavitation. [PERSON] [9] compared three widespread cavitation models in the evolution around an NACA0015 hydrofoil based on the level set method. The results offer the optimal selection of cavitation models at different conditions. [PERSON] [10] investigated the cavitation phenomenon around the asymmetric leading edge (ALE) 15 hydrofoil through large eddy simulation, and the modified Schnerr-Sauer cavitation model was employed, which considers the influence of incompressible gas. [PERSON] [11] numerically analyzed the strong and weak interactions between neighboring cavitation bubbles with a revised single-component multiphase Lattice Boltzmann method.