细长体出水动力学的实验研究及数值模拟

航行体出水过程涉及到气液两相交界,流场是非定常且高度非线性的,是一个非常复杂的过程。为了深入研究该问题,采用实验和数值模拟相结合的方法研究了细长体垂直出水过程的水动力特性。实验在二维水箱中进行,采用高速摄影仪拍摄了不同速度下细长体垂直出水流场。数值模拟采用 VOF 模型,结合动网格和 UDF 技术对相应的实验工况进行了模拟。研究了细长体水下运动过程中空泡的生长和溃灭机理,以及细长体出水时对自由液面的干扰规律。实验研究表明:(1)细长体在完全出水时刻出水速度发生突增;(2)随着细长体速度的增大,空泡产生的部位是从尾部开始,然后再在头部出现;(3)当细长体头部没有局部空泡产生的时候,细长体出水时会造成明显液面隆起现象,当细长体头部产生局部空泡后,细长体出水时,没有明显液面隆起现象,但是会产生“喷溅”现象。数值计算表明:在不产生空泡的情况下,细长体头部接近水面到完全出水的过程中,自由液面都会隆起,尾部出水时液面隆起的程度比头部出水时大。通过比较数值计算结果与实验结果,两者吻合较好。

Experimental and numerical study on hydrodynamic characteristics in water-exit of slender body

The water-exit process of a vehicle involves severe gas-liquid mixing,and the flow field is unsteady and highly nonlinear.To understand the characteristics of the process,the water-exit process of high speed slender body is studied by experimental and numerical simulation.The experiment was operated in a two-dimensional water tank,and the flow field of the water-exit of a slender body with different velocities was photographed by a high speed camera.The water-exit process according to the experiment was simulated,the Volume of Fluid(VOF)model was used to simulate the interface between water and air,and the dynamic mesh and UDF technology were adopted to simulate the movement of the slender body.The growing process of the cavity,the mechanism of the cavity collapse,and the way of the slender body affecting the free surface when the slender body moving in the water have been investigated.The experimental result indicates that:(1)there is a sudden increase in velocity when the slender body completely leaves water;(2)as the velocity increases,the cavity phenomenon begins to appear at the end of the slender body,and subsequently appears at the head of the slender body;(3)if the velocity is not large enough to generate local cavity at the head of the slender body,the free surface uplifts obviously as the slender body exits from the water.If the local cavity appears at the head of the slender body,the free surface uplift phenomenon is unobvious,and the “splash”phenomenon appears. The numerical result indicates that the free surface uplift phenomenon endures for the whole water-exit process,and the extent of free surface uplift is larger when the tail leaves water than the head.The numerical result was found to be in agreement with the experimental results.