球体入水空泡演变和运动特性影响试验研究

为了探究表面粗糙度对球体入水空泡演变及运动特性的影响，基于实验室开放水槽试验系统，选取了5种表面粗糙度的球体，使用高速摄像机记录入水过程，并得到了各个球体的入水空泡、喷溅的演变过程以及运动特性的变化。发现入水空泡和喷溅的闭合都会给球体一个负方向的加速度。通过对比不同表面粗糙度球体的位移、速度、加速度曲线，发现表面粗糙度最大的球体在砰击阶段结束后，其速度会明显小于其他球体，并且表面粗糙度对球体运动的影响主要体现在入水早期。分析了上述各球体的入水空泡闭合后，与自由面相连的空泡的收缩运动，发现其收缩速度和加速度曲线均会出现极大值点，呈现出球体表面粗糙度越大出现得越早的趋势。

Experimental study on the cavity evolution and motion characteristics of spheres into water

Water-entry experiments were carried out by adopting five kinds of surface roughness to explore the effects of surface roughness of water-entry spheres on the evolution of cavities induced the water-entry of the spheres and the motion characteristics of the spheres during the water-entry process of the spheres. The experiments were based on an open water-tank test system. Meanwhile, a high-speed camera was used to record the water-entry processes of the spheres with different surface roughness. The evolutions of cavity, splash and motion characteristics of each sphere were obtained. It is found that the closure of cavity and splash will exert a negative acceleration on the sphere. By comparing the displacement, velocity and acceleration curves of the spheres with different surface roughness, it is found that the sphere with the largest surface roughness will move significantly slower than other spheres after the end of slamming, and that the effects of surface roughness on the sphere motion are mainly reflected in the early period of the water-entry. By analyzing the shrinkage of the cavities connected with the free surface of each sphere after cavity seal, it is found that both the shrinking velocity and acceleration curves take on extreme points, and that the larger the surface roughness of the spheres, the earlier the extreme point appears.