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

利用水下激波聚焦过程中产生的超高压驱动脉冲式高速液体射流，进行了实验尝试。为了更详细地了解所涉及的流场，特别是高压的产生过程，还进行了数值模拟。为了利用微炸药产生理想的球形水下冲击波，已经做了许多努力。结果，我们成功地用10mg叠氮化银点燃100mg PETN，获得了高于8000bar的最大压力。在初步实验数据的基础上，我们制造了一个高速液体射流，由约2100巴的高压驱动。高压发生在长、小轴为212mm X 150mm的椭球形腔的第二焦点处，这是由于水下冲击波的聚焦造成的，该冲击波是通过点燃放置在腔第一个焦点处的10mg叠氮化银产生的。如果在椭球腔的外侧设置一根带喷嘴的圆形管，在第二焦点处，我们可以通过该喷嘴获得高速脉冲液体射流。我们用自制的PVDF压力表测量了由于射流冲击而产生的滞止压力，得到其最大值约为90bar，脉宽为2mus。相应的液体射流冲击速度可估计为130m/s左右。脉冲液体射流具有工作空间极小、工作时间极短（2-3mus）的优异特点，在不久的将来应促进其在医学和其他科学领域的应用。

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.