Effect of head cone angle on flow field variation during high-speed projectile water entry
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摘要: 弹体高速入水过程中会发生空化现象形成空泡,引起流场变化,进一步影响弹体运动稳定性。针对不同头部锥角双锥段弹体穿越自由液面后的流场变化影响特性展开研究,基于电磁发射装置进行弹体高速入水试验,采用重叠网格技术和流体域体积(volume of fluid,VOF)多相流模型建立弹体高速入水数值模型并展开计算,通过试验验证了数值模型的有效性,获取了不同头型弹体垂直入水后的流场变化特性。研究发现:双锥段弹体垂直入水后,空泡对称发展,空泡面闭合后,总长度增大,最大宽度逐渐减小;随着弹体空化器头部锥角的增大,弹体入水初期空泡闭合、表面沾湿的位置向尾部靠近,空泡轮廓越宽,入水瞬间和水中运动时的阻力也越大,速度衰减越快,空泡发生面闭合的时间越迟,水中运动同一时刻,弹体尾空泡的长度越长,水域内涡结构的长度越短。Abstract: During the high-speed water entry of a projectile, cavitation occurs, forming a cavity bubble that alters the flow field and subsequently affects the projectile’s motion stability. Our study investigates the characteristics of flow field changes after double-cone projectiles with different head cone angles traverse the free surface. High-speed water entry experiments were conducted by using an electromagnetic launch device, and a numerical simulation model of high-speed water entry was established basing on the overset mesh technique and the volume-of-fluid multiphase flow model. The validity of the simulation model was verified through experiments, and the flow field characteristics after the vertical water entry of projectiles with different head types were obtained. The research findings are as follows: After the vertical water entry of a double-cone projectile, the cavity bubble develops symmetrically. Following surface closure of the cavity bubble, its total length increases while its maximum width gradually decreases. As the head cone angle of the projectile's cavitator increases: during the initial entry phase, the closure point and wetted surface position move closer to the tail; the cavity contour becomes wider; the resistance experienced at the moment of entry and during underwater motion increases, leading to faster velocity decay; the time of surface closure for the cavity bubble is delayed. At the same moment during underwater motion, the longer the length of the tail cavity bubble, the shorter the length of the vortex structures within the water domain.
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Key words:
- high-speed water entry /
- cavity bubble /
- projectile /
- head type
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表 1 不同时刻各弹体入水初期空泡最大宽度
Table 1. The maximum width of the cavitation at the initial stage of each projectile entering the water at different times
弹体模型 空泡最大宽度/mm 1 ms 2 ms 3 ms 4 ms 5 ms 6 ms 60°锥头 64.10 75.71 106.06 110.89 116.66 123.25 90°锥头 74.37 89.45 103.19 114.11 120.42 124.90 120°锥头 82.98 103.82 114.55 126.38 134.49 136.10 150°锥头 86.88 106.97 120.82 133.87 138.11 147.02 平头 90.16 110.06 125.19 137.44 144.93 153.83 表 2 弹体入水后速度、压力变化
Table 2. Variation of velocity and pressure of projectiles after entering the water
弹体模型 入水5 m后速度/(m·s−1) 速度衰减/(m·s−1) 入水瞬间头部顶点峰值压力/MPa 入水5 m后头部顶点压力/MPa 60°锥头 99.3 10.7 5.1 3.47 90°锥头 103.5 6.5 7.7 4.58 120°锥头 101.9 8.1 12.6 5.08 150°锥头 100.6 9.4 17.9 5.17 平头 99.5 10.5 22.7 5.09 -
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