Mechanism of Generation of High Speed Liquid Jet Driven by High Pressure due to Underwater Shock Wave Focusing and Its Application

利用水下冲击波聚焦产生的超高压驱动液体脉冲高速射流进行了实验研究，并进行了数值模拟，详细了解了流场，特别是高压产生过程。为了使用微型炸药产生理想的球形水下冲击波，人们做了许多努力。结果表明，用10 mg叠氮化银点燃100 mg PETN，得到的最大压力超过8,000 bar，并在此基础上，利用2,100 bar的高压驱动，产生了高速液体射流。在长、短轴为212 mm × 150 mm的椭圆形空腔的第二个焦点处产生高压，这是由于水下冲击波的聚焦引起的，该冲击波是通过点燃放置在空腔第一个焦点处的10 mg叠氮化银产生的。在第二焦点处设置一个带有喷嘴的圆管，通过该喷嘴可获得高速脉冲液体射流，用国产PVDF压力计测量了射流冲击引起的滞止压力，最大值约为90巴，脉宽约为2 μ s。脉冲液体射流具有工作空间小、工作时间短（2- 3 μ s）等优点，在医学和其它科学领域的应用将得到进一步的推广。

An experimental attemp was made to produce a pulsed high-speed liquid jet driven by ultra high pressure generated during underwater shock wave focusing.A numerical simulation was also carried out to know the flow field concerned in detail, especially to make clear the process of high pressure generation. Much efforts had been performed in order to produce an ideally spherical underwater shock wave by using a microexplosive. As a result, we succeeded in getting a maximum pressure higher than 8,000bar with 100mg PETN ignited by 10mg silver azide.Based on the data obtained from a preliminary experiment, we tritato produce a high-speed liquid jet, driven by a high pressure of about 2,100bar. The high pressure occurred at the second focal point of an ellipsoidal cavity with the major and minor axes of 212mm X 150mm, due to focusing of an underwater shock wave, which was generated by igniting 10mg silver azide placed at the first focal point of the cavity. If a circular pipe with a nozzle, provided at an outer side of the ellipsoidal cavity, is set at the second focal point, we can obtain a high-speed, pulsed, liquid jet through this nozzle.We measured stagnation pressure due to impact of the jet by means of a home -made PVDF pressure gauge, and obtained it as the maximum value of about 90bar and pulse width of 2mus. The corresponding impact velocity of a liquid jet can be estimated as about 130m/s.A pulsed liquid jet has such excellent feature that working space and time are extremely small and short (2-3mus), so that its application to medical and other scientific fields should be promoted in the near future.