# Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle
## 1 Introduction
[20] used a two-equation curve to determine the outdoor profile of the nozzle cavity based on the Helmholtz nozzle, and the experimental analysis results showed that the designed nozzle had good flushing efficiency. [PERSON] et al. [21] developed a nozzle of swirling cavitating jet for natural gas hydrate, and the experimental results confirmed the flow field characteristics and erosion performance of the nozzle. [PERSON] et al. [22] compared the CFD calculation results using the RANS SST K-u turbulence model with the experimental results and found that the cavitation onset was sensitive to the nozzle geometry. The cavitation onset may be different for the same cavitation number. However, the above literature focuses on improving the accuracy of numerical models to observe the subtle flow of water jets, which not only improves the accuracy of results but also increases the difficulty of calculation. This is helpful to the theoretical development of fluid mechanics but neglects the optimization of the nozzle structure in engineering applications. In practical applications, the nozzle needs to be optimized in advance by numerical simulation and then installed by a target distance experiment. Therefore, the numerical simulation should have a certain precision but not time-consuming calculation. If the physical properties of the jet are the same as those of the surrounding medium, it is a submerged jet; if not, it is a nonsubmerged jet [23]. In general, the submerged jet with water as the fluid medium refers to the underwater jet. The cavitation nozzle, as a cavitation-generating element, directly affects the cavitation effect of the jet [24]; thus, it is significant to carry out research on it. Although the existing literature has discussed the jet and cavitation characteristics of the cavitation nozzle under submerged and nonsubmerged conditions, the focus is mostly on the accuracy of the model, and the optimization of the nozzle structure has no practical application. In this paper, we have designed and optimized a cavitation nozzle for underwater creature removal and established the three-dimensional (3D) physical model of the angular cavitation nozzle in the submerged state by using CFX fluid simulation software. The main purpose of the study is to optimize the structure of the cavitation nozzle by using the CFD technique. The effect of mixture density on cavitation is orderly discussed under the multiphase mixture model. The feasibility of this model is verified by relevant experimental data. Then, the velocity distribution, pressure distribution, and vapor volume fraction distribution of the flow field inside and outside the nozzle in the computational domain could be derived by solving the RNG \(k\)-\(\varepsilon\) model and homogeneous cavitation model. We aimed to investigate in depth the effect of the nozzle inlet contraction section, cylindrical section, and outlet expansion section on the cavitation effect of the jet in the submerged state, to improve the degree of cavitation of the angular cavitation nozzle, and to provide a basis for the study of water jet cavitation.