圆柱体入水空泡壁面运动特性与空泡演化关系实验研究

为了获得入水空泡壁面的运动特性与空泡演化之间的关系,进而对入水空泡演化过程开展定量划分研究。采用高速摄像的方法对低弗劳德数条件下的圆柱体入水开展实验研究。通过对比具有水平速度的圆柱体以不同倾角入水空泡,分析了入水空泡壁面运动特性与空泡演化过程的关系,并基于空泡壁面运动特性划分空泡演化各阶段,分析了空泡演化在各阶段的流动机理。实验研究结果表明:空泡壁面的运动特性与空泡演化过程紧密关联,根据空泡壁面位移和运动速度变化规律可定量划分空泡演化阶段。空泡的闭合形式对于具有水平速度的圆柱体入水所形成的空泡的演化过程有显著影响,若空泡发生表面闭合,则空泡演化包含了空泡敞开、空泡体积膨胀、空泡拉长以及溃灭后四个阶段,无量纲分界时间分别为T=2.8、T=5.4和T=6.9;若空泡发生深闭合,则其演化过程仅包含空泡敞开、空泡闭合以及空泡溃灭三个阶段,并以时间T=2.8和T=8.4为分界。根据空泡壁面的运动特性划分空泡演化各阶段的时间特性非常明确且没有相互重叠。

Tests for relationship between cavity evolution and motion characteristics of cavity wall during a cylinder entry into water

The present study aims to address the water entry cavity evolution of cylinder with lower Froude number. For this purpose, an experiment on water entry cavity of a cylinder with different inclined angles and horizontal velocities is conducted by utilizing a high-speed video camera. The cavity flow phenomena induced by the complex movement cylinder is obtained from the video, and the relationship between cavity evolution and the motion characteristic of cavity wall is analyzed by contrast. The phases of impact water entry cavity are divided according to its motion characteristic. The experimental results demonstrate that, the motion characteristic of cavity wall is closely related to the cavity evolution, so the phases of cavity evolution can be quantitatively divided through the motion characteristic of cavity wall. The cavity evolution is affected seriously by its closure type. There are four phases for the cases that the surface seal occurs, namely, open-cavity, expand-volume cavity, stretch-cavity, and closed-collapsing cavity respectively, and the corresponding boundary time is T=2.8, T=5.4, and T=6.9. When the cases only occur deep seal, the evolution process includes three phases, open-cavity, closed-cavity, and collapsing-cavity respectively. The boundary time for those cases is T=2.8 and T=8.4. The overlapped part doesn’t exist in each cavity evolution phases by the divided way of the motion characteristic of cavity wall.