表面疏水圆柱体低速入水冲击与流体动力学特性研究

Water entry of objects is a common phenomenon in marine engineering, such as water entry of torpedo and water entry of trans-media aircraft and so on. Under some circumstances, object can be wrapped by cavity which affects its underwater motion. However, the influence mechanism of cavity on water entry has not been identified. There are several factors influencing the resistant force on object during water entry, including gravity, buoyancy, fluid resistance, the pressure inside cavity, the motion of object and so on, which make this problem complex. Besides, recent year’s research shows that the generation of cavity is not only related to its velocity and head shape, but also relevant with its surface property. Therefore, this project aims to obtain the water entry impact and hydrodynamics of a hydrophobic cylinder under low-speed, and explore the influence of cavity acting on the cylinder. The main research contents include: (1) research on the water entry impact and motion of a hydrophobic cylinder; (2) research on the water entry hydrodynamics of a hydrophobic cylinder; (3) study the influence of head shape on the water entry of a hydrophobic cylinder.

物体入水问题研究具有广泛的工程背景和深刻的科学内涵。物体入水时会受到流体的阻力作用，在有空泡的情况下，物体进入水中并被空泡包裹后，受重力、浮力、流体阻力、空泡内压力以及物体速度变化等因素的影响，阻力变得非常复杂；空泡对物体运动的影响机理尚未完全明确，而近年来又发现空泡的产生与物体的表面性质密切相关。因此，本项目拟以表面疏水圆柱体为研究对象，通过高速摄影实验，研究物体低速入水的冲击响应及运动规律、流体的飞溅、空泡等流体动力学行为，探索空泡演化对物体入水运动的影响机理。本项目的主要研究内容包括：（1）表面疏水圆柱体低速入水的冲击和运动特性；（2）表面疏水圆柱体低速入水的流体动力学特性；（3）头部形状对表面疏水圆柱体低速入水的影响研究。

物体入水时能够将空气带入水中形成空泡，尤其是具有疏水表面的物体，更容易在入水的过程中形成空泡，而空泡的演化将对物体的运动产生影响。本项目以疏水物体作为研究对象，采用高速摄影实验方法，研究了低速情况下，疏水球形颗粒和疏水圆柱入水过程中的冲击响应及运动规律、流体的飞溅、空泡等流体动力学行为。通过实验设计和理论分析，得到了球形颗粒物在邦德数和韦伯数参数空间下的不同空泡运动和闭合行为，解释了空泡的形成机理。在此基础上，针对圆柱的垂直入水情况，主要考察了表面浸润性和头部形状对空泡发展和演化的影响，针对圆柱的水平入水情况，主要考察了密度比的变化对空泡发展和演化的影响。研究表明：表面浸润性、头部形状、密度比等因素都将对圆柱入水的空泡行为产生影响，主要表现在初始空泡的形状以及后续的空泡闭合方面，其本质原因与接触线的移动特性有关。上述这些基础性研究结论，可为物体的跨介质入水问题研究提供参考和基础性技术支撑。