During the landing and recycling on the sea surface of a spacecraft or rocket, a concave structure may impact on the water surface. In the present paper, we experimentally and numerically analyze the multiphase flows and transient impact load during the oblique water entry of the concave-nose projectile. The projectiles used in the experiments consist of a main body that embeds an acceleration measurement system, and a transparent concave-nose. Firstly, free surface evolutions and cavity dynamics are given for the concave-nose projectile, which shows significant changes compared with the projectile without concave-nose. A special jet inside the concave-nose during the formation of the air-entertainment cavity is observed. Subsequently, it is found that compared with the projectile without concave-nose in the early stage. The increase rate of the axial force of the concave-nose projectile is slower and the force curve has a steep drop stage, then they enter the uniform reduction stage. As the concave depth increases, a ‘double-peak’ phenomenon on the axial force curve appears. It is found that the force peak is transferred to a single peak with increasing the impact velocity. The force peak of the concave-nose projectile is greater than the projectile without concave-nose. Besides, with increasing the concave depth, the maximum axial force of the concave-nose projectile increases firstly, and then decreases. When the ratio of concave depth to inner diameter is greater than 2, the influence of concave depth on the peak value of axial force is small. Moreover, the pressure distributions of the fluid domain and the concave-nose are analyzed to reveal the mechanism of the variation of the force peak. The study is able to provide a basic reference for the analysis of the recycling of the rocket, aircraft, etc.

中文翻译：

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凹头弹斜入水瞬态冲击载荷试验与数值研究

航天器或火箭在海面着陆和回收时，凹形结构可能会撞击水面。在本文中，我们对凹鼻弹斜入水过程中的多相流和瞬态冲击载荷进行了实验和数值分析。实验中使用的弹丸由嵌入加速度测量系统的主体和透明的凹形弹头组成。首先，给出了凹鼻弹丸的自由表面演化和空腔动力学，与无凹鼻弹丸相比，其显示出显着的变化。在空气娱乐腔形成过程中，可以观察到凹鼻内有一种特殊的射流。随后发现与早期无凹鼻的弹丸相比。凹鼻弹丸的轴向力增加速度较慢，力曲线有一个陡峭的下降阶段，然后进入均匀减小阶段。随着凹进深度的增加，轴力曲线上出现“双峰”现象。研究发现，随着冲击速度的增加，力峰值转移到单峰。凹鼻弹丸的力峰值大于无凹鼻弹丸。此外，随着凹深度的增加，凹头弹丸的最大轴向力先增大，然后减小。当凹进深度与内径之比大于2时，凹进深度对轴向力峰值的影响较小。此外，还分析了流体域和凹鼻的压力分布，揭示了力峰值的变化机制。该研究可为火箭、飞机等回收分析提供基础参考。