Pressure fluctuation and surface morphology induced by the high-pressure submerged waterjet confined in a square duct

Abstract

Driven by high pressures, the submerged waterjet is featured by high velocity and cavitation, which arouse unsteady flow signals. To elucidate the temporal and spatial characteristics of the high-pressure submerged waterjet, an experimental work was carried out with the waterjet submerged in a square duct and jet pressures varied from 50 to 320 MPa. Three nozzles with different throat-segment diameters were considered. Under non-impingement condition, pressure fluctuations near the waterjet stream were acquired with miniature dynamic pressure transducers. For the jet impingement cases, microhardness, surface morphology and mass removal rate of the impinged specimens were measured. The results show that drastic change of pressure in ambient water is caused by the waterjet. As the jet pressure rises, high-frequency components are excited and the effect of cavitation is significant. In streamwise direction, the gap between the first, second and third highest frequencies is progressively narrowed. The maximum pressure amplitude increases as waterjet develops, irrespective of the jet pressure and the nozzle diameter. High jet pressures lead to high microhardness of the target surface. Surface morphology serves as an indicator of the synthetic effect of jet impingement and cavitation. Erosion patterns associated with the three nozzles are considerably different; cavitation erosion intensity declines with the increase in the nozzle diameter.