Experimental study on oblique water-entry of projectile constrained by ice hole
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摘要: 基于高速摄影技术，开展了冰孔约束条件下的弹丸倾斜入水实验；通过对比分析无冰环境与冰孔约束条件下的弹丸入水运动过程，并将入水运动过程分为空泡扩张、空泡闭合以及空泡溃灭三个阶段进行了研究，得到了冰孔约束条件下弹丸入水的空泡演化特性；通过对比同一直径冰孔约束条件不同入水初速下弹丸的空泡演化过程及速度变化规律，总结得出了入水初速对于冰孔约束条件下弹丸空泡演化特性以及入水运动特性的影响规律。研究结果表明：空泡扩张阶段，冰孔约束条件下产生的喷溅较为分散，弹丸背水面产生部分隆起；此外，冰孔约束条件下的空泡扩张受到阻碍，空泡最大直径减小。空泡闭合阶段，冰孔约束条件下的空泡闭合时间提前，并且撞击冰板的反射流冲击空泡侧壁使空泡发生局部冲击溃灭。空泡溃灭阶段，冰孔约束条件下的溃灭尾迹由局部冲击溃灭、脱落溃灭和正常溃灭组成；空泡溃灭产生的尾迹旋涡较小。随着入水初速的提高，空泡的长度和最大直径明显增大，局部冲击溃灭的宽度增加；冰孔约束条件会使得弹丸在空泡扩张阶段的速度衰减幅度增大，空泡的闭合时间提前，开始溃灭的时刻延后。Abstract: Based on high-speed photography technology, an experiment study on water-entry of oblique projectile constrained by ice hole was conducted. Digital image processing technology was employed to extract the experimental data. The water-entry process of oblique projectile was analyzed under both ice-free and ice hole constraint environment, and the water-entry process is divided into three stages: cavity expansion stage, cavity closure stage and cavity collapse stage. Additionally, a series water-entry experiments were also conducted with different initial velocities of projectiles under the same ice hole constraint, allowing for the establishment of a relationship between initial velocity and ice hole constraint. Results show that during the cavity expansion stage, the free surface under the ice-hole constraint does not form a bulge, and the splashing on the water-away side of the projectile is suppressed by the ice hole and is more dispersed. The ice-hole constraint leads to the obstruction of cavity expansion and the appearance of bending on the left side of the cavity near the free surface, the maximum diameter of cavity decreases. In the cavity closure stage, the closure time of the cavity is advanced under the constraint of the ice hole. The reflected flow impacts the right side of cavity wall, which causes the pinch-off and local collapse of the cavity. During the cavity collapse stage, under the constraint of ice hole, the wake of cavity collapse consists of local impact collapse, pinch-off cavity collapse and normal cavity collapse, and the wake vortex generated by the collapse is small. As the initial velocity increases, the length and maximum diameter of the cavity significantly increase, and the width of local impact collapse also increases. Furthermore, the ice hole constraint makes the projectile velocity decay faster during the cavity expansion stage, advances the closure time of the cavity, and delays the collapse time of the cavity.
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图 5 空泡扩张阶段空泡演化照片
Figure 5. Photos of cavity evolution in water-entry cavity expansion stage
图 7 空泡扩张阶段（3.72 ms）仰视照片
Figure 7. Photos of cavity expansion stage (3.72 ms) from bottom view
图 11 不同初速下弹丸的入水过程
Figure 11. Projectile water-entry processes at different initial velocities
图 12 闭合以及溃灭时刻的空泡细节
Figure 12. Diagram of cavity detail at cavity closure and collapse moment
图 13 不同入水初速下的空泡演化轮廓图
Figure 13. Cavity evolution contours at different initial velocities
图 14 不同工况下的弹丸速度变化曲线
Figure 14. Projectile velocity attenuation under different working conditions
图 15 不同工况下弹丸的加速度变化曲线
Figure 15. Projectile acceleration curves under different working conditions
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