# Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle
## 1 Introduction  
Cavitation water jet technology is one of the effective fouling prevention methods that has received widespread attention in recent years [1; 2; 3]. It has the advantages of energy saving and environmental protection, high cleaning efficiency, no damage to equipment surfaces, and easy mechanization and automation. A representative application example of the cavitation water jet is underwater organism removal [4; 5]. Issues on cavitation water jets mainly concern water jet flow characteristics, cavitation nozzle optimization, and erosion performance enhancement. In general, the analysis of cavitation water jets is carried out by experiments and numerical simulation. Through experiments, the performance of cavitation nozzles can be enhanced not only by observing the erosion effect [6; 7] but also by visualization through high-speed photography and acoustic emission [8]. [PERSON] et al. [9] established cavitation efficiency expressions, and the experimental analysis showed that the nozzle diameter and injection distance have a large effect on the kinetic energy and specific energy consumption. [PERSON] et al. [10] used the frame-difference method to analyze the dynamic evolution of the cavitation cloud and obtain the range of concentrated cavitation collapse. The best target distance range was determined by the verification test of cavitation water blasting of 2A12 aluminum alloy. [PERSON] et al. [11] established a high-pressure cavitation jet experimental system and conducted high-speed photographic experiments. It was found that the periodic time-frequency of cavitation development could be better reflected by the proper orthogonal decomposition (POD) method. [PERSON] et al. [12] concluded that the mixture composition of the flowing medium (liquid, steam, and air) has a particular influence on the size and pulsation frequency of the cavitation cloud by observing the dynamic behavior of the cavitation cloud in the flow of a converging-diffusing nozzle with a rectangular cross-section. [PERSON] et al. [13] used high-speed imaging to characterize the development andcollapse of the cavitation cloud inside the nozzle and its connection with surface erosion, showing that cavitation vortex shedding occurs in a periodic manner. [PERSON] et al. [14] evaluated the cavitation effect by measuring the specimen weight change, showing that acoustic emission monitoring is a promising tool. As an effective supplement to research tools, numerical simulation by means of computers can reproduce experimental scenarios without laboriously setting up the experimental platform. Numerical simulation can also yield accurate results and, therefore, is favored by researchers. In the research on cavitation water jet based on numerical simulation, [PERSON] et al. [15] conducted a numerical study of the underwater high-pressure cavitation water jet with Reynolds-averaged Navier-Stokes (RANS)-large eddy simulation (LES) hybrid model to reveal the relationship between the shear cavitation formation mechanism and the turbulence structure and velocity distribution characteristics in the jet. [PERSON] et al. [16] used a mass transfer cavitation model and a modified RANS k-u model to study the structure of cavitation nozzles under various operating conditions, revealing that the re-entrant jet is the main cause of shedding cavitation and destruction of O-type cavitation. [PERSON] et al. [17] predicted the jet flow by the Zwart-Gerber-Belamri (ZGB) model and found that simulation results using compressible assumptions are in better quantitative and qualitative agreement with experimental data. [PERSON] et al. [18] developed a hybrid optimization algorithm combined with CFD techniques to improve the cavitation effect of nozzles in deep water. [PERSON] et al. [19] studied the effect of differently shaped nozzles on cavitation performance, and the numerical simulation results showed that the hydraulic diameter at the nozzle outlet has a high correlation with the gas phase distribution after cavitation. [PERSON] et al.