A shadowgraph visualization system of shock waves caused by water-entry projectiles and its experimental research
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摘要: 扩大成像视野对于开展充水容器中弹体入水冲击波传播及弥散方面的可视化研究具有重要的实际意义。阴影成像技术适用于大视野实验，且对流场冲击波和扰动的可视化研究具有简单性和通用性，其中直接阴影成像最为简单，但可靠点光源的缺乏是阻碍其发展应用的瓶颈。因此基于国产短弧氙灯管，自制了短弧氙灯点光源，根据阴影成像原理，设计出一种弹体入水冲击波阴影成像可视化系统，详细介绍了其组成和运行原理。利用该系统对高速弹体入水进行了试验研究，获得了弹体入水冲击波的阴影成像和冲击波信号的压力时程曲线，通过阴影成像和冲击波信号相结合分析了弹体入水冲击波的传播特性，并进行了理论验证。结果表明：该弹体入水冲击波阴影成像可视化系统具有可靠性和设计的合理性。弹体高速入水后，初始冲击波的强度最大，随着冲击波的传播，冲击波强度逐渐降低，水中冲击波的传播速度不断降低，球形冲击波的半径逐渐增大。Abstract: It is of great practical significance to expand the imaging field for the visualization research of shock wave propagation and dispersion caused by water-entry projectiles in water-filled tank. The shadowgraph technique is suitable for large field experiments, and the visualization of shock waves and disturbances in the flow field is simple and universal. Among them, the direct shadowgraph technique is the simplest, but the lack of reliable point light sources is the bottleneck hindering its development and application. Therefore, based on domestic short-arc xenon lamps a self-made short-arc xenon lamp point light source was designed. According to the principle of shadowgraph, a shadowgraph visualization system of shock waves caused by water-entry projectiles was designed, and its composition and operating principle were introduced in detail. The system had been used to conduct experimental research on high-speed water-entry projectiles. A shadowgraph technique was employed to visualize the shock wave generated by the water-entry projectile in a water-filled tank. Besides, by extracting pixel points from high-speed photos and calibrating the geometric dimensions in the photos, a spatial coordinate system was established to describe the motion of the projectile and shock wave. Simultaneously, the pressure time history curve of shock wave signal was obtained by means of the acquisition equipment of shock wave signal. With the combination of shadowgraphs and shock wave signals, the propagation characteristics of the shock wave produced by the water-entry projectile were analyzed, and they were verified by theoretical calculations. The results show that the reliability and rationality of the visual system of the shock wave generated by the water-entry projectile are demonstrated. After the projectile enters the water at a high speed, the initial shock wave has the highest intensity. As the shock wave propagates, the shock wave intensity gradually decreases, the propagation speed of the underwater shock wave continues to decrease, and the radius of the spherical shock wave gradually increases.
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图 2 弹体入水冲击波的阴影成像可视化系统
Figure 2. Shadowgraph visualization system of shock waves caused by water-entry projectiles
图 4 球形弹体出炮口产生的冲击波
Figure 4. The shock wave generated by the spherical projectile exiting the gun
图 5 弹体入水及空泡扩展过程
Figure 5. Processes of the projectile entering the water and its cavity expansion
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