Cavitation and Wear in the Micro Jewel Nozzle of Ultra-High Pressure Water Jet

In an ultra-high pressure water jet cutting system, the micro jewel nozzle has important influences on the machining efficiency. Cavitation inside the jewel orifice affects the jet formation directly and is a crucial reason for the nozzle wear. By simulating the cavitation flow in the orifice at pressure within 400 MPa, the jet formation process in the nozzle was expounded. The influence of pressure, the aspect ratio and the inlet shape of orifice on the cavitation and jet were also analyzed. At the same time, an experiment was carried out to study the nozzle wear. The results show that the cavitation region in orifice reduces along the nozzle axis with the increasing of the aspect ratio. Moreover, the cavitation region can reach the nozzle outlet when the aspect ratio is smaller than a certain value. At this condition, the jet initial diameter is smaller than the orifice diameter and increases with the increase of pressure. The orifice inlet with a streamline design can effectively restrict the cavitation development. The wear in the jewel orifice inlet due to the cavitation and water erosion is much more severe than in the outlet and is more serious under higher operating pressure. Accordingly, it is useful to select a appropriate aspect ratio for reducing the erosion in the nozzle.