中文摘要：

阐述了水下超声速气体垂直过膨胀射流的准二维实验研究和射流的数值计算结果。利用高速摄影仪在1000帧/s的拍摄速度下实时记录了过膨胀工况下水下垂直射流的喷射状态,清晰显示了水下气体垂直射流的演化过程;并利用专业软件FLUENT,对实验Laval喷嘴内外纯气相流场进行了数值计算,发现喷口附近存在复杂激波区,辅助分析了水下高速气体垂直射流的动态不稳定性形貌。实验与计算表明：在保持较小射流流量和保障较大马赫数的条件下,水下超声速垂直射流在水环境中引发的回击频率会得到减弱;准回击现象的发现证实了这一结论。这对于工程应用中的风口材料的＂空蚀效应＂的减弱提供了理论依据。

英文摘要：

Quasi-two-dimentional submerged vertical over-expanded supersonic jets were studied experimentally and numerically.The gas-jet flow patterns under over-expanded conditions were recorded at real time by a high-speed camera at the rate of 1000 frames/s.The development process of supersonic gas jets and the process of the instable flow pattern were visualized clearly.The pure gas flow field inside and outside the Laval nozzle used in the experiment was numerically simulated by FLUENT,and results dedicate a complex shock wave region existing out of the nozzle exit.The simulation results are instrumental in understanding the unstable pattern of submerged vertical supersonic jet flow as an aided reference.The experimental and simulation results indicate that,the frequency of back-attack will be reduced at the operating conditions of relatively small mass flow and a high Mach-number,and this is proved by the discovery of quasi-back-attack phenomenon.The finding in the paper provides an available theroretical reference for weakening or eliminating the cavitation erosion in engineering application field.