航行体回收垂直入水空泡流场及水动力特性研究

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.