航行体回收垂直入水空泡流场及水动力特性研究

NUMERICAL INVESTIGATION ON CAVITY STRUCTURES AND HYRODYNAMICS OF THE VEHICLE DURING VERTICAL WATER-ENTRY

航行体以尾部向下姿态入水过程的研究对无动力运载体以及导弹回收等问题的解决具有重要意义.本文采用VOF (volume of fluid)多相流模型,并结合动网格技术,对航行体尾部向下姿态高速垂直入水过程展开研究.数值计算结果与实验[12]吻合度较好,验证了本文所采用数值方法的准确性与可行性.以航行体为研究对象,分析了航行体垂直入水过程中流体动力、入水空泡及流场结构的演变特性,进而讨论了入水速度对流体动力特性和入水空泡的影响规律.研究结果表明:在航行体入水过程中主要受到压差阻力的影响,在入水冲击阶段,航行体所受阻力系数在撞击自由液面时达到最大,随着入水时间的推移,总阻力系数缓慢降低,最终趋于稳定,空泡发生溃灭时产生微小波动.在入水空泡发展的过程中,在惯性力与内外压差的共同作用下,空泡壁面会同时存在扩张与收缩两种阶段.航行体垂直入水过程中阻力系数峰值随着入水速度的增大而增大,且随着速度的增大,空泡最大直径以及空泡收缩速率增大.空泡面闭合无量纲时间以及深闭合时入水空泡夹断深度与入水深度的比值随弗劳德数变化基本不变.

The study of the water-entry behavior of the vehicle with the tail downward is of great significance to many engineering problems,such as recycle of unpowered vehicles and missiles.In this paper,the VOF homogeneous flow model is combined with dynamic mesh technique to study the vertical water-entry process of the vehicle.Good agreement has been obtained between the experimental and numerical results on the water-entry velocity and trajectory.The evolution of the hydrodynamic characteristics,the cavity patterns and the flow structures during the vertical water entry process is analyzed.The results show that the whole water entry process can be divided into four stages:the moment of contact,the open cavity stage,the surface seal stage and the deep seal stage.The pressure drag plays a major role during the water entering process,and the drag coefficient reaches to the maximum in the moment of contact stage when the vehicle touches the free surface.With time evolution,the drag coefficient is gradually decreasing,and tends to be stable in final.A slight fluctuation occurs when the cavity is collapsing.The influence of water-entry velocities on the hydrodynamics and cavity patterns is also studied.During the vertical water-entry of the vehicle.With the increase of the water-entry velocity,the peak of the drag coefficient increases and the maximum dimensionless cavity diameter and the cavity shrinking rate increase.Moreover,the dimensionless moments of the surface seal and deep seal during the vertical water-entry process are almost the same with the different Froude number,as well as the ratio of the depth of the cavity pinch-off to the depth of the vehicle in the deep seal.