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流场演化过程是揭示激光推进机理的重要研究内容之一。利用纹影系统和PCO-HSFC高速相机,首次拍摄了自来水诱导CO2激光击穿空气产生的激波向空气和水中的演化过程。阐述了产生两次气蚀空穴的原因:初始时刻产生的空穴为激波作用于水面所致,第二次空穴出现在相机被触发后约8μs时,是激光烧蚀水蒸气作用于水面所形成的低压区。实验结果表明:击穿后流场向激光入射方向(空气中)演化较快,激波初速度较大,约为6km/s;流场向水中演化相对较缓,激波初速度约为3.33km/s。两者都服从指数衰减,分别在约73.368μs和41.649μs时衰减到声速。研究结果对于把水作为工质应用于激光推进有一定意义。
The evolution of flow field is one of the important research contents to reveal the mechanism of laser propulsion. Using a profiling system and a PCO-HSFC high-speed camera, the first shot of tap water induces the evolution of shock waves into the air and water produced by CO2 laser penetrating air. The reasons for producing two cavitation cavities are described: the cavities generated at the initial time are caused by the shock waves acting on the water surface, the second cavities appear at about 8 μs after the camera is triggered, and laser ablation water vapor acts on Low pressure area formed by the water surface. The experimental results show that the flow field changes sharply to the laser incident direction (air) after breakdown, and the initial shock velocity is about 6 km / s. The evolution of the flow field is relatively slow and the initial shock velocity is about 3.33 km / s. Both obey the exponential decay and decay to the speed of sound at about 73.368 μs and 41.649 μs, respectively. The research results have some significance for the application of water as a working medium for laser propulsion.