Abstract In this paper, the results of an experimental investigation of the normal impact of grooved spheres on a calm water surface are presented. Particular attention is given to describe the air cavity formation when the number of grooves and the impact velocity change. All experimental tests are conducted in a constant surrounding fluid Bond number, Capillary length using grooved spheres with constant diameter but in various impact, Reynolds and Froude numbers, and the trajectory of spheres is visualized by a high-speed camera at 1 ∼ 2 kfps frame rate. This study extends the recent paper (Mehri and Akbarzadeh, 2020) that first investigated the water entry of grooved spheres, by considering higher impact velocities. The study introduces the role of grooves in the air entrainment cavity formation and shows the dependence of the cavity characteristic such as upper and underlying cavity shape, vertical upward and downward reentrant jets, and splash curtain shape on the number of grooves and the impact velocity. Also, the effect of the number of grooves on and sphere kinetics like descent trajectory, velocity, and acceleration is discussed.

中文翻译：

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凹槽球体的水进入：凹槽数量和冲击速度的影响

摘要 在本文中，介绍了凹槽球体对平静水面的法向冲击的实验研究结果。特别注意描述了凹槽数量和冲击速度变化时的气腔形成。所有的实验测试都是在恒定的周围流体邦德数、毛细管长度使用具有恒定直径但在各种冲击下的凹槽球体、雷诺数和弗劳德数下进行的，球体的轨迹由高速相机以 1 ∼ 2 kfps 帧进行可视化速度。这项研究扩展了最近的论文（Mehri 和 Akbarzadeh，2020 年），该论文首先研究了凹槽球体的水进入，考虑了更高的冲击速度。该研究介绍了凹槽在加气空腔形成中的作用，并显示了空腔特征，如上空空腔形状、垂直向上和向下的折返射流以及飞溅帘形状对凹槽数量和冲击速度的依赖性。此外，还讨论了凹槽数量对下降轨迹、速度和加速度等球体动力学的影响。