倾斜放置圆柱体入水流体动力特性实验研究

doi:10.16183/j.cnki.jsjtu.2019.116

摘要/Abstract

摘要：

为了研究倾斜放置的圆柱体垂直入水过程流体动力特性，针对低弗劳德数条件下的圆柱体入水开展实验研究．采用高速摄像技术记录圆柱体入水过程空泡演化以及圆柱体的位置．基于数字图像处理技术，提取圆柱体入水过程的运动轨迹以及倾角变化．对数据进行五阶光滑样条拟合处理，获得圆柱体的速度和加速度，进而开展圆柱体的运动特性和动力特性研究．研究结果表明：倾斜放置圆柱体垂直入水过程形成空泡分离、双空泡等独有的流动现象．圆柱体砰击自由液面后加速度快速增加，并在空泡分离后达到最大值，随后迅速减小并逐渐趋向于0.倾角越大的圆柱体入水后竖直速度衰减越快，而水平速度则快速增加．然而不同初始倾角圆柱体的轨迹均呈现先向迎流方向运动后向背流方向运动的特征．圆柱体的角加速度对水动力的响应非常快，整体呈现先增加后减小的变化特性．初始倾角越大的圆柱体入水后角速度增加越快且达到的最大值也越大，其倾角增加也越快．圆柱体的阻力系数和升力系数在入水后快速增加，而在空泡闭合后增加缓慢，且初始倾角大的圆柱体入水后力系数增加较快．

关键词: 倾斜放置圆柱体, 入水, 流体动力特性, 实验研究

Abstract:

Experiments of vertical water entry for a cylinder with different inclined angles are performed at a low Froude number to investigate the cavity evolution and hydrodynamics. Unique phenomena of double cavities and separated cavity are observed. The accurate trajectories and attitude angles for the inclined cylinders are proposed, which are extracted by utilizing the method of digital image correlation from the image sequence recorded by a high-speed camera. The raw data of trajectory and attitude angle are fitted using the method of quintic smoothing spline, with which, the velocity and acceleration of the cylinders during water entry are estimated, and the cylinder characteristics of motion and hydrodynamic force are studied. The experimental results demonstrate that the unique cavity phenomena are observed for the inclined cylinder during water entry, such as cavity separation and double cavities. The acceleration increases quickly after the cylinder penetrates into water and achieves the maximum value after cavity separation occurs. After that, the acceleration decreases quickly and tends to zero. The vertical velocity of the cylinder with a large initial inclined angle decreases faster than that with a small inclined angle, while the corresponding horizontal velocity increases rapidly. The trajectories of the cylinder with different initial inclined angles generally present the characteristics of first moving in the upstream direction and then in the downstream direction. With respect to the properties of inclined angle, the angular acceleration responds very quickly to the hydrodynamic force, and it generally first increases and then decreases. In addition, the angular speed of cylinder for a large initial inclined angle increases faster than that for a small inclined angle. The inclined angle shows the same trend as well. The cylinder drag and lift coefficients rapidly increase after the cylinder enters the water, and then slowly increase after the cavity pinches off. Moreover, the force coefficients increase more quickly for the cylinder with a large initial inclined angle.

Key words: inclined cylinder, water entry, hydrodynamics, experimental investigation

中图分类号:

TV131.2

夏维学, 王聪, 李佳川, 侯东伯. 倾斜放置圆柱体入水流体动力特性实验研究[J]. 上海交通大学学报, 2021, 55(1): 67-76.

XIA Weixue, WANG Cong, LI Jiachuan, HOU Dongbo. Experimental Investigation on Motion Hydrodynamics of Water Entry for Inclined Cylinders[J]. Journal of Shanghai Jiao Tong University, 2021, 55(1): 67-76.

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