Cavitation in Submerged Water Jet at High Jet Pressure

Abstract

Recent industrial applications have unfolded a promising prospect for submerged water jet. Apart from widely acknowledged water jet properties, submerged water jet is characterized by the formation and complex evolution of cavitation bubbles. These bubbles not just alter the flow behavior of submerged water jet but also pose a profound effect upon impinged solid surface. At low jet pressures, some conclusions associated with submerged water jet have been acquired, while studies at high jet pressures have rarely been reported. From today’s view, both numerical and experimental approaches manifest apparent limitations in the presence of high-pressure submerged water jet. Consequently, validation of numerical results cannot be implemented conveniently due to lack of relevant experimental results. The major purpose of the present study is to explore cavitation features in submerged water jets with jet pressures of 120 and 150 MPa. Numerical techniques are utilized to locate cavitation zone in submerged water jet stream and to delineate cavities as well. Meanwhile, velocity distribution in the jet stream is obtained to calculate jet kinetic energy. Under submerged conditions, bubbles disperse rapidly in ambient water and therefore impede the penetration of incident light. Thus submerged water jet stream cannot be distinguished accurately. Such a difficulty encountered in optical flow measurement and flow visualization for submerged water jet seems insurmountable. Thus experimental efforts are devoted to an interpretation of cavitation effect through examining surface morphology features of the solid sample impinged by submerged water jet. And these features are obtained quantitatively using an optical profiling system. The results show that the occurrence of cavitation depends largely on the shear effect between fluid layers with different velocity magnitudes. Annular cavity shape is typical for submerged water jets. The existence of cavitation can be maintained within a limited streamwise distance from the nozzle. Furthermore, different jet pressures result in considerably different cavitation severity and effective streamwise lengths of cavity. According to the footprints on the impinged sample surface, it can be concluded that the impingement effect is ascribed to both cavitation effect and jet kinetic energy. The footprint produced on the target surface is in accordance with that predicted with numerical techniques in terms of size and shape. Several important aspects associated with the cavitation phenomenon in the submerged water jet are clarified in the present study.