# A Study of Cavitation Erosion in Artificial Submerged Water Jets
## 2 Numerical Simulation
### Effects of Dimensionless Standoff Distance between Nozzle and Workpiece  
Figure 4 illustrates the velocity contour map and vapor volume fraction distribution at different standoff distances between the nozzle and workpiece in the flow field. As shown in Figure 4, it is evident that as the standoff distance of the artificially submerged cavitation water jet increases, the core jet beam within the jet flow field extends further. Due to spatial limitations, the number and size of cavitation clouds within the flow field decrease at shorter standoff distances. At a dimensionless standoff distance of \(S_{D}\) = 20, the core jet beam approaches the workpiece surface inside the flow field. Only a small number of smaller cavitation clouds are produced in the flow field, indicating that due to the limitations of the standoff distance, the initial cavitation bubbles within the flow field fail to grow completely before contacting the workpiece surface and thus collapse. At dimensionless standoff distances of \(S_{D}\) = 30 and \(S_{D}\) = 40, the number and volume of cavitation clouds inside the flow field increase, providing conducive conditions for the growth and development of initial cavitation bubbles and space. At a dimensionless standoff distance of \(S_{D}\) = 50, the cavitation cloud within the flow field remains a certain distance away from the workpiece surface, indicating that fully developed cavitation nuclei are likely to collapse before contacting the workpiece surface. In brief, standoff distance that is either too short or too long may diminish the cavitation generated within the flow field and its consequential impact on the workpiece surface. Due to the unsteady characteristics of cavitation clouds and the potential impact of time on numerical simulation results, further exploration of the distribution patterns of cavitation clouds in the artificially submerged cavitation jet flow field at different time points is necessary. The periodic variation in vapor volume fraction distribution in the flow field is depicted in Figure 5 when the dimensionless standoff distance is \(S_{D}\) = 20. For short target distances, cavitation clouds within the flow field exhibit fewer numbers and smaller volumes at different time points. The Space limitations prevent initial cavitation bubbles from experiencing optimal development conditions and growth processes within the flow field. The initial cavitation bubbles in the flow field rapidly contact the wall, leading to their collapse and dissipation. Figure 3: Variation in velocity and pressure at point A and point B for different numbers of meshes. At the dimensionless standoff distance of \(S_{D}=30\), the periodic variation in vapor volume fraction distribution in the flow field is depicted in Figure 6. Compared to \(S_{D}=20\), both the number and volume of cavitation clouds within the flow field increased at this dimensionless standoff distance. An evident periodic pattern is observed in the development process of cavitation clouds within the flow field. At \(T=4\Delta T\), initial cavitation bubbles emerge within the flow field. Over time, cavitation bubbles gradually enlarge, forming larger cavitation nuclei within the flow field, as depicted in Figure 6 at \(T=36\Delta T\). Figure 4: (**a**) Velocity contour map and (**b**) vapor volume fraction distribution at different dimensionless standoff distances between the nozzle and workpiece in the flow field. Figure 5: Periodic variation in vapor volume fraction distribution in the flow field when \(S_{D}=20\). Figure 6: Periodic variation in vapor volume fraction distribution in the flow field when \(S_{D}=30\).