Abstract The critical initial angle of attack that the cylinder can move along the non-circuitous trajectory in water entry is investigated experimentally and numerically. A primary focus is on characterizing the relationship between the initial inclined angle α0 and horizontal velocity u0 in the parameters space of α0∼u0/v0, where u0/v0 is the horizontal velocity u0 to vertical velocity v0 ratio. To build a dense initial parameter space to capture the accurate critical curvature boundary (CCB), which is the critical parameters of the cylinder moving along a non-circuitous trajectory, a substantial water entry experiment is performed for the cylinder with different initial inclined angles and horizontal velocities. In this experiment, a high-speed camera is employed to record the position and the inclined angle of the cylinder. In addition, a large eddy simulation method is used to simulate some particular water entry cases that the cylinder initial parameters are near the CCB space. After the analysis, the initial parameter space for the oblique water entry almost locates in the left circuitous space. Based on the equation of the oblique water entry in the parameter space of α0∼u0/v0, an empirical equation of CCB is established by giving a correction item of deviation angle of attack. When the initial parameters of the cylinder satisfy the equation of CCB, the cylinder first moves along the initial line Lu and then along the offset line Ld. The offset distance doffset between these two lines first increases with α0 and u0/v0 and then gradually tends to a constant about doffset/D = 1, where D is the diameter of the cylinder. Moreover, the simulation results indicate that the pressure distribution on the cylinder surface is affected by the impact velocity, the wettability of the cylinder surface, the initial angle of attack and the distance between the cylinder surface and the pinch-off location.

中文翻译：

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圆柱入水非迂回轨迹临界攻角及相应冲击腔

摘要 通过实验和数值方法研究了圆柱体在入水时沿非迂回轨迹运动的临界初始攻角。主要关注在参数​​空间α0∼u0/v0 中表征初始倾斜角α0 和水平速度u0 之间的关系，其中u0/v0 是水平速度u0 与垂直速度v0 的比值。为了建立一个密集的初始参数空间来捕捉精确的临界曲率边界（CCB），这是圆柱体沿非迂回轨迹运动的临界参数，对具有不同初始倾斜角和水平速度。在本实验中，采用高速摄像机记录圆柱体的位置和倾斜角度。此外，采用大涡模拟方法对圆柱初始参数接近CCB空间的一些特殊进水情况进行模拟。经分析，斜入水的初始参数空间几乎位于左侧迂回空间。基于参数空间α0∼u0/v0中斜入水方程，通过给出偏差迎角修正项，建立CCB经验方程。当圆柱的初始参数满足 CCB 方程时，圆柱首先沿初始线 Lu 移动，然后沿偏移线 Ld 移动。这两条线之间的偏移距离doffset首先随着α0和u0/v0而增加，然后逐渐趋于一个常数，大约doffset/D = 1，其中D是圆柱的直径。而且，