Xiaolong Ding

Effects of area discontinuity at nozzle inlet on the characteristics of self-resonating cavitating waterjet

The current research on self-resonating cavitating waterjet(SRCW) mainly focuses on the generation mechanism and structure optimization. Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available. In order to further improve the performance of SRCW, effects of area discontinuity(enlargement and contraction) are experimentally investigated using three organ-pipe nozzles. Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects. The results reveal that area enlargement and contraction affect the peak differently, depending on the inlet pressure, nozzle geometry, and standoff distance; while area contraction always improves the amplitude regardless of these factors. At inlet pressures of 10 MPa and 20 MPa, area discontinuity improves the peak at almost all the testing standoff distances, while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa. The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure. Moreover, the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance, depending on the type of area discontinuity and nozzle geometry. A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed. The proposed research provides a new method for effectively enhancing the performance of SRCW.

Effects of the geometry of impinging surface on the pressure oscillations of self-resonating pulsed waterjet

A preliminary experimental investigation was performed with a focus on the axial pressure oscillations of self-resonating pulsed waterjet under different impinging surfaces. Five target plates of different impinging surfaces were impinged by self-resonating pulsed waterjets at various standoff distances and under four inlet pressures. It was found that the geometry of impinging surface significantly affects the pressure oscillation peak and amplitude of self-resonating pulsed waterjet, and the influences largely depend on the inlet pressure. Both the pressure oscillation peak and the amplitude increase to their maximum and then drop with increasing standoff distance, which is regardless of the geometry of impinging surface. But the geometry influences the values of the optimum standoff distance and the oscillation peak and amplitude. Compared with the trend of pressure oscillation peak against standoff distance, the oscillation amplitude can be more obviously changed by the impinging surface. Moreover, an assumption that the geometry affects the pressure oscillation peak by the rebound waterjets and hydroacoustic waves has been proposed based on related literature. Further study should be conducted to clarify the relations between the axial pressure oscillation and the geometry of impinging surface.

Experimental Investigation on Surface Quality Processed by Self-Excited Oscillation Pulsed Waterjet Peening

High-speed waterjet peening technology has attracted a lot of interest and is now being widely studied due to its great ability to strengthen metal surfaces. In order to further improve the mechanical properties of metals, self-excited oscillation pulsed waterjets (SOPWs) were used for surface peening with an experimental investigation focused on the surface topography and properties. By impinging the aluminum alloy (5052) specimens with SOPWs issuing from an organ-pipe oscillation nozzle, the hardness and roughness at various inlet pressures and stand-off distances were measured and analyzed, as well as the residual stress. Under the condition of optimum stand-off distances, the microscopic appearances of peened specimens obtained by SEM were displayed and analyzed. Results show that self-excited oscillation pulsed waterjet peening (SOPWP) is capable of improving the surface quality. More specifically, compared with an untreated surface, the hardness and residual stress of the peened surfaces were increased by 61.69% and 148%, respectively. There exists an optimal stand-off distance and operating pressure for creating the highest surface quality. SOPWP can produce almost the same enhancement effect as shot peening and lead to a lower surface roughness. Although such an approach is empirical and qualitative in nature, this procedure also generated information of value in guiding future theoretical and experimental work on the application of SOPWP in the industry practice.