# A Study of Cavitation Erosion in Artificial Submerged Water Jets
## 2 Numerical Simulation
### Effects of Dimensionless Standoff Distance between Nozzle and Workpiece
While the periodicity of cavitation clouds remains relatively unchanged at this juncture, an examination of their distribution reveals a reduction in the number of cavitation clouds. This indicates that the initial cavitation bubbles within the flow field have commenced collapsing and shrinking independently after undergoing a full growth and development stage before engaging with the workpiece surface for  
Figure 8: Periodic variation in vapor volume fraction distribution on the workpiece surface when \(S_{D}=20\). Figure 9: Periodic variation in vapor volume fraction distribution on the workpiece surface when \(S_{D}=30\). impact. Consequently, the internal cavitation effect in the flow field at this point is not as pronounced as when \(S_{D}=30\). With an increase in the dimensionless standoff distance, the distribution of cavitation clouds near the wall diminishes, consequently weakening the cavitation effect. At \(T=16\Delta T\), the figure depicts the reappearance of a point-like cavitation cloud like that observed at \(T=0\) in the central area of the workpiece surface. In comparison to the annular cavitation cloud formed in the central area near the workpiece surface at the dimensionless standoff distance of \(S_{D}=30\), both the volume and number of cavitation clouds have decreased. This reduction indicates a decrease in the continuity and density of the cavitation cloud distribution on the workpiece surface. With the gradual increase in the dimensionless standoff distance, the cavitation effect of the cavitation cloud on the workpiece surface initially undergoes enhancement before gradually diminishing. This observation indicates that the dimensionless standoff distance that is excessively long exerts a more pronounced adverse effect on the cavitation effect compared to one that is too short. Effects of Nozzle Structure and High-Pressure Inlet Condition at Different Dimensionless Standoff Distance between the Nozzle and Workpiece  
In this section, we investigate the influence of various dimensionless standoff distances on the cavitation effect induced by artificially submerged cavitation water jet using the mass loss method. Simultaneously, we analyze the impact of alterations in the high-pressure inner nozzle pressure and nozzle structural parameters on the erosion effect on the workpiece surface. Initially, the inlet pressure of the high-pressure inner nozzle is modulated via a frequency converter while maintaining the low-pressure outer nozzle pressure at \(P_{L}=0.02\) MPa. The erosion period spans 30 min, facilitating the generation of influence curves delineating alterations in the inner nozzle pressure and the dimensionless standoff distance, affecting both the mass loss of the workpiece and the dimensionless standoff distance of the artificially submerged cavitation water jet across various structural parameters. To avoid the influence of the errors generated during the experiment on the accuracy of the results, each group of experiments was conducted three times under the same conditions. When the high-pressure inner nozzle pressure is set to \(P_{H}=5\) MPa, illustrated in Figure 11, the workpiece mass loss \(\Delta m\) progressively rises with the incremental dimensionless standoff distance, reaching a peak at \(S_{D}=30\), after which it rapidly declines. Prior to \(S_{D}\leq 30\), it is evident that at \(\delta=30^{\circ}\) and \(\beta=30^{\circ}\), the heightened shear between the two jet beams results in an increased formation of primordial cavitation bubbles within  
Figure 10: Periodic variation in vapor volume fraction distribution on the workpiece surface when \(S_{D}=40\). the flow field, intensifying the cavitation effect exerted by the jet on the workpiece surface. Conversely, at \(S_{D}\) = 40 mm, with \(\delta=0^{\circ}\) and \(\beta=0^{\circ}\), the cavitation effect on the specimen is most pronounced.