Flow characteristics and structure response of high-speed oblique water-entry for a revolution body

Abstract

The high-speed water-entry process of a revolution body involves fluid and structure interaction, which is a complex nonlinear and unsteady process. The revolution body with high speed is subjected to extreme impact load at the moment of hitting water surface which would cause great deformation or even damage to the structure. In order to investigate the physical understanding of the structural strength of revolution bodies and the mechanism of the cavity dynamics during high-speed water-entry process, a fluid-structure interaction (FSI) model based on a co-simulation progress between STAR-CCM+ and ABAQUS was adopted. The model performed a two-way interaction analysis which can consider the influence of the deformation of structure to fluid into. In the form of CFD analysis, a three-dimensional simulation with a six-degree-of-freedom model was carried out, in which the Shear Stress Transfer (SST) turbulence model and the volume of fluid (VOF) technique were used for turbulence computation and air-liquid interface tracking, respectively. In the part of FEM research, the shell mesh form with a whole Johnson-Cook material model was implemented to give a full consideration of deformation process and the accuracy of structure computation, which can effectively reflect the plastic deformation of structure. Firstly, a comparison between FSI result and experimental result of the high-speed water-entry process was conducted. The results show that the velocity attenuation, displacement and the cavity features are in good agreement with the experimental result, which proves two-way FSI method can be effectively applied into the research of high-speed water-entry problem. Then a numerical simulation of revolution body oblique water-entry with different velocity was carried out. The results show that the stress initially focuses on the edge of the bottom side of the revolution body, then it transports to the central area, remaining steady in the end. Compared with the results of rigid body, the peak value of impact load of the flexible body appears smaller due to the repeated deformation for buffer, which also causes the fluctuation of the load curve. After the initial water impacting, the cavity presents an asymmetric shape. As water-entry time increases, the asymmetry of cavity becomes weaker. In the process of 60 m/s oblique water-entry, surface closure of the cavity occurs. With the increase of water-entry velocity, the time of cavity surface closure takes longer. The peak value of the impact load whose period is quite short appears immediately at very beginning of water-entry process. After entering the water surface, the impact load of the revolution body decreases dramatically and rapidly and fluctuates slightly. The peak value of the impact load is related to water-entry velocity. The higher the velocity is, the earlier peak value of the impact load occurs and more obviously it fluctuates. As water-entry velocity exceeds 100 m/s, plastic deformation appears in the central area of bottom of revolution body.