## 4 Conclusions  
By establishing a numerical model of the hydrodynamic cavitation generator and numerically simulating its internal flow field, the pressure field, the velocity field and the cavitation bubble volume fraction were analyzed. The effects of different structural parameters on the cavitation performance were investigated in this study. The following conclusions are drawn from this study:  
1. A novel shear hydrodynamic cavitation generator is designed to solve the problem of wastewater treatment. The moving and fixed teeth of the cavitation generator are crossed, not pairs of teeth. The numerical model was established based on the mass conservation equation and momentum conservation equation, and the Mixture model, realizable k-\(\epsilon\) turbulence model, and Zwart cavitation model were used to describe the internal flow field. Experiments were conducted using wastewater from a printing and dyeing plant as the medium, among which the degradation rate of COD in water is taken to characterize the cavitation feature of the device. It was found that the cavitation performance increased with the increase in rotational speed. The cavitation performance decreases as the treatment volume increases. Thus, the applicability and accuracy of the mixture multiphase flow and Zwart cavitation model for the shear-type hydrodynamic cavitation generator were validated. 2. The laws governing the effect of different structural parameters on the cavitation performance are compared. Different structural parameters have a significant impact on the cavitation performance of the cavitation inducer with the number of teeth rows exerting the most noticeable influence. As the number of tooth rows increases, the volume fraction of cavitation bubbles rises. Once the number of tooth rows reaches eight, a stable low-pressure field forms inside the cavity, resulting in a stable cavitation performance. Conversely, an increase in the tooth number in a single row reduces the flow space for fluid within the cavitation inducer, leading to a decrease in cavitation performance. Furthermore, an increase in the outer diameter of the cavitation inducer enhances its centrifugal force, causing an increase in circumferential velocity and consequently increasing the shear velocity between teeth, thereby improving cavitation performance. The presence of tooth tilt alters the location of cavitation bubble generation between teeth, facilitating cavitation action on the fluid. Additionally, with an increase in the tilt angle, the low-pressure area between teeth enlarges, leading to a corresponding increase in cavitation performance. 3. The cavitation between the rotated teeth is mainly formed by the centrifugal force field under extremely strong negative pressure. The cavitation between the fixed teeth by the fluid caused by the high-speed rotation of the circumferential velocity increases, bringing an increase in the shear velocity between the rotated and fixed teeth; the static pressure decreases, resulting in a localized negative pressure between the teeth and the formation of cavitation. Therefore, the size of the flow space of the fluid in the hydrodynamic cavitation generator has a great impact on the hydrodynamic cavitation generator effect as well as its shape. Figure 18: Velocity cloud of 85\({}^{\circ}\) tooth level angle. **Author Contributions:** Conceptualization, F.L., M.T. and X.Z. ; methodology, F.L., M.T. and S.H. ; software, F.L., M.T. and F.Z. ; validation, F.L. and M.T. ; formal analysis, F.L., M.T. and S.H. ; investigation, F.L., M.T. and X.Z. ; resources, F.L. and M.T. ; data curation, F.L., M.T. and S.Z. ; writing--original draft preparation, M.T. ; writing--review and editing, F.L. and M.T. ; supervision, F.L. ; project administration, F.L. ; funding acquisition, F.L. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by grants from the Jiangsu Provincial Graduate Student Research and Practice Innovation Program Project (Grant No.