中文摘要：

宝石喷嘴是影响超高压水射流切割系统工作效率的重要部件,而宝石内部的空化直接影响射流的形成,也是宝石磨损的重要原因之一。对400 MPa压力范围内宝石孔内部的空化两相流进行了数值模拟,阐述了射流在宝石内的形成过程,分析了长径比、压力和入口形状对宝石内空化的影响,并在相应压力下对宝石喷嘴的磨损进行了实验研究。结果表明：宝石内部的空化发展程度随着长径比的增大而减弱;在一定的长径比范围内,空化可以发展到喷嘴出口,并最终使射流的初始直径小于喷嘴直径,且在此条件下当压力升高时,射流的初始直径增大;良好的入口形线可以降低空化的发展程度;宝石入口的磨损较出口更显著,空蚀和高压水的冲蚀造成了宝石孔边缘形状的破坏,这种破坏随着压力的升高而加剧,选择合适的长径比是减少冲蚀磨损的有效途径。

英文摘要：

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.