中文摘要：

水切割射流的动力学特性的诸多方面尚未得到认识和理解。本文对毛细喷孔产生的超高压水射流展开可视化研究，分析了常规压力及超高压条件下毛细水射流的液体破碎机制并对超高压毛细射流的脉动现象进行了讨论。常规条件下的毛细射流遵从经典的破碎模式；在超高压条件下，射流完整段呈瑞利模式，完整段以下呈雾化破碎模式，射流集束性呈现周期性变化。结果表明，传统理论不能够表达小孔径时超高速毛细水射流的破碎特性；喷孔内部流动情况如流动分离及空化成为该条件下射流破碎和脉动的重要原因。

英文摘要：

The physical phenomena involved in cutting jets remain covered. This study carries out experiments to capture the appearance of ultra-high pressure water jet issued from a fine orifice. The jet breakup modes under normal pressures are compared with the one at ultra-high pressures. The surface fluctuation of cutting jets is demonstrated. It shows that the capillary jet at low a pressure break up in classical modes, however, at the extreme pressure, its intact portion is in Rayleigh mode while the downstream part consists with atomization mode. Furthermore, the jet coherency varies as the intact length fluctuates with time. These results lead to the conclusion that typical theory can not accurately depict the ultra-high speed capillary jet. It can be also inferred that the flow separation and cavitation inside the orifice has a predominate effect on jet instability and breakup.