# A Study of Cavitation Erosion in Artificial Submerged Water Jets
## 2 Numerical Simulation
### Effects of Dimensionless Standoff Distance between Nozzle and Workpiece
This suggests that while augmenting the outer convergent angle can enhance the cavitation intensity within the flow field, it also somewhat impedes the full development of cavitation bubbles within the flow field. When the high-pressure inner nozzle pressure \(P_{H}\) = 10 MPa, as shown in Figure 12, the workpiece mass loss \(\Delta m\) exhibits the same trend characteristics with a gradual increase in the dimensionless standoff distance, and the peak loss occurs at \(S_{D}\) = 30. Similarly, regardless of the dimensionless standoff distance, the cavitation effect on the workpiece surface produced by the nozzles with three structural parameters is intensified with the pressure elevation of the high-pressure inner nozzle, with the best elevation effect at \(\delta=30^{\circ}\) and \(\beta=30^{\circ}\). At \(S_{D}\) = 40, the cavitation effect is best when the nozzle structural parameters are \(\delta=0^{\circ}\) and \(\beta=0^{\circ}\); as the pressure of the high-pressure inner nozzle is elevated, the cavitation phenomenon inside the flow field is strengthened, the cavitation cloud's action distance is lengthened, and the cavitation effect is more intense. When the high-pressure inner nozzle pressure \(P_{H}\) = 15 MPa, as shown in Figure 13, all the structural parameters of the artificially submerged water jet on the workpiece surface erosion effect are substantially improved. As observed in the figure, when \(S_{D}\) = 10, the artificial submerged cavitation jet flow field is mainly generated by the initial cavitation bubbles from the high-pressure nozzle outlet occupying a dominant position. The two beams of the jet do not completely converge, and the strong shear effect between the jet does not occur completely. So, although there is a certain amount of cavitation effect on the workpiece surface, small erosion pits are formed. As the pressure of the inner nozzle at this point is relatively high, the depth of the etching pit on the workpiece surface is larger, which is due to the high pressure of the jet dominating and limiting the growth and development of time and space; the high-pressure inner nozzle outlet of the initial cavitation bubbles on the workpiece surface only play a small part of the role. At \(S_{D}\) = 50, the workpiece surface is farther from the nozzle outlet. The flow field inside the initial cavitation bubbles after the full development may have collapsed before contacting the surface of the workpiece surface, and only a small portion of the cavitation bubble successfully strikes the workpiece, resulting in cavitation. As can be seen in Figure 13, the workpiece surface at this point presents a wide range of scattered erosion pits, and the depth of the pits is not large. This  
Figure 6.0 Variation in mass loss with dimensionless standoff distance for artificially submerged cavitation water jet nozzle at different structural parameters when \(P_{H}\) = 5 MPa. indicates that with an increase in the dimensionless standoff distance, the jet gradually diffuses outward. The flow field inside the cavitation bubble spreads to the surroundings, and it is difficult for the high-pressure core of the jet beam to act on the workpiece surface. At this point, the pits of the workpiece surface are mainly formed by the shear effect of a large number of cavitation bubbles. However, due to the excessively long dimensionless standoff distance, the cavitation strength is greatly reduced. Figure 6.1 Variation in mass loss with dimensionless standoff distance for artificially submerged cavitation water jet nozzle at different structural parameters when \(P_{H}=10\) MPa. Figure 6.2 Variation in mass loss with dimensionless standoff distance for artificially submerged cavitation water jet nozzle at different structural parameters when \(P_{H}=15\) MPa.