Effects of Nozzle Inner Surface Roughness on the Performance of Self-Resonating Cavitating Waterjets under Different Ambient Pressures

Abstract

The self-resonating cavitating waterjet (SRCW) has been widely used for many practical and industrial applications since the first recognition of its strong cavitation ability. To further improve the performance of SRCW under ambient pressures, the effects of nozzle inner surface roughness were experimentally studied by impinging the jets on pure aluminium specimens (1070A) at various standoff distances. The typical macroscopic appearances and mass losses of the eroded specimens were used to evaluate the performances of the jets issuing from six organ-pipe nozzles of different inner surface roughness values (0.8 μm, 1.6 μm, 3.2 μm, 6.3 μm, 12.5 μm, and 25 μm). The results show that nozzle inner surface roughness significantly influences the optimum standoff distance and the cavitation intensity, which greatly depends on the ambient pressure. Moreover, it is found that there is always an optimum surface roughness that can remarkably enhance the cavitation erosion capability under each ambient pressure. Specifically, at ambient pressures of 2 MPa and 4 MPa, the surface roughness of 6.3 μm causes the strongest cavitation intensity at standoff distances of 42 mm and 50 mm, respectively. While at ambient pressures of 6 MPa, 8 MPa, and 10 MPa, the surface roughness of 12.5 μm is the one that maximally enhances the intensity at standoff distances of 45 mm, 40 mm, and 35 mm, respectively. Furthermore, the enhanced cavitation intensity is found to improve the impingement power of the high-speed waterjet as well. The present study also helps to provide a guideline for determining the finishing accuracy of inner surface required in the fabrication of organ-pipe nozzles.

The Effects of the Downstream Contraction Ratio of Organ-Pipe Nozzle on the Pressure Oscillations of Self-Resonating Waterjets

“…A schematic diagram of the experimental setup for measuring the axial pressures of SRWJs under different values of the downstream contraction ratio is shown in Figure 2. It should be noticed that the experimental method and the main equipment and facilities shown in the figure were all the same with those used in our previous investigations [25][26][27][28][29][30][31][32], except for the organ-pipe nozzles. Therefore, the schematic of the experimental set-up is the same as the previous ones [31,35].…”

“…where Ma is the Mach number, defined as the ratio of the flow velocity to the local sound speed, Ma = U e /c. Finally, by applying the Bernoulli equation [27] and Equation (4), the chamber lengths can be achieved, which were 21 mm and 15 mm, corresponding to the two inlet pressures of 10 MPa and 20 MPa. With respect to the pressure loss across the nozzle, more detailed information of the calculation process can be found in our previous research [27,35].…”

“…Ding et al [25] took advantage of SRWJs to improve the mechanical properties of the aluminum alloy and claimed that the hardness and residual stress could be increased by 61.69% and 148%, respectively. In addition, the authors have already conducted a series of experiments on SRWJs, such as the effects of the nozzle inner surface roughness, feeding pipe diameter, and the area discontinuity at the nozzle inlet on the characteristics of pressure oscillations and cavitation erosion of the jet [26][27][28][29][30][31][32][33][34][35].…”

“…Despite a great many investigations on SRWJ, it should be noticed that the optimal values of the downstream contraction ratio of organ-pipe nozzles are still unknown and need to be studied. So far, the organ-pipe nozzles used in the research are all manufactured using an equation that only gives the ratio of the chamber length to the exit diameter [13][14][15][16][17][18][19][20][21][22][25][26][27][28][29][30][31][32], and the detailed physical parameters required for fabricating an effective nozzle have not been reported.…”

Research on Surface Roughness of Hardox Steels Parts Machined by Abrasive Waterjet

“…The state of the focusing tube has been also studied [19]. The most critical parameter of influence was determined to be the surface roughness of the tube.…”