# Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle
## 4 Conclusions  
Numerical simulation is a significant instrument to observe the flow features of the internal and external flow fields of angular cavitation nozzles, which can more effectively obtain the cavitation law of the jet. In this paper, combined with the influence of mixture density on cavitation, the structure of the cavitation nozzle has been optimized based on CFD technology, and a simulation model has been verified by relevant experiments. By considering the effect of angular cavitation nozzle structure on jet cavitation, it can be concluded that with a 20 MPa incident pressure and \(d=2.5\) mm, the maximum steam volume fraction of the angular cavitation nozzle can reach 0.95 when the nozzle structure parameters are \(\alpha=13.5^{\circ}\), \(Ld=3d\), \(Le=4d\), and \(\beta=60^{\circ}\). At this point, the nozzle has the best cavitation effect.  
The cavitation jet of the angular cavitation nozzle presents a vortex ring shape. Cavitation bubbles are generated from the near wall surface of the expansion section where the maximum steam volume fraction appears. The steam volume fraction is small on the axis and gradually increases along the radial direction. It is more accurate and reliable to judge the cavitation effect by the axial steam volume fraction distribution at \(d/2\).  
The expansion section of the angular cavitation nozzle is the low-pressure area of the fluid and also the place where cavitation bubbles are generated and developed. Optimizing the structure of the expansion section can lead to a better cavitation effect.  
Next, we will build an experimental platform guided by numerical simulation. On the one hand, we can further verify the feasibility of numerical simulation; on the other hand, we can obtain the best target distance of the nozzle through experiments to prepare for the application of the nozzle. The grid adaptation based on the gradient of the volume fraction indeed is a great meshing method. However, it is difficult to implement this grid adaptive technology in CFX software. This technology will be studied in our future work.  
Conceptualization, W.D. and W.L.; methodology, W.D.; software, W.D.; validation, W.D., L.Y. and W.L.; formal analysis, W.D.; investigation, W.D.; resources, W.D., L.Y. and W.L.; data curation, W.L.; writing--original draft preparation, W.D.; writing--review and editing, L.Y. and W.L.; visualization, W.D.; supervision, L.Y. and W.L.; project administration, L.Y.; funding acquisition, L.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China, grant no. 2022 YFB4702401 and Fuzhou Institute of Oceanography, grant no. 2021F11.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors would like to thank the anonymous reviewers for their constructive suggestions, which comprehensively improved the quality of the paper. The authors also would like to thank the support from Fuzhou Ocean Research Institute and the support from the Fujian Provincial College Marine Engineering Equipment Design and Manufacturing Engineering Research Center.  
The authors declare no conflict of interest.