Investigation of the tail-slapping load and trajectory stability of a trans-media vehicle during high-speed oblique water entry

During the high-speed water entry, the trans-media vehicle goes through multiple tail-slapping, which may cause damage to the main structure and its accessories. The bending moment induced by tail-slapping phenomenon may also lead to the trajectory instability of the trans-media vehicle. Based on the VOF multiphase flow method, the study of the load characteristics of the main body and attached structures of the trans-media vehicle and its accessories in the stages of the generation, development, and collapse of cavity under the condition of inclined water-entering with an attack angle has been conducted. The influence of the water entry inclination angle on the tail-slapping load, cavity collapse load and the trajectory stability are revealed. The results show that the cavity collapse stage is the most dangerous working condition during the water entry process. As the water entry inclination angle increases, the axial and normal forces on the structure increase in the cavitation collapse stage, while the normal overload coefficient approaches a constant. When the inclination Angle into the water increased from 60° to 90°, the pitch moment coefficient of the structure increased by 47.1%. A larger inclination angle can reduce the axial and normal loads of the horizontal rudders during the cavity collapse stage, and also improve the trajectory stability of the vehicle. However, it will increase the axial loads of the vertical rudders at the same time. When the cavity wall impacts the tail of the trans-media vehicle during the cavity collapse stage, the three-directional rotation of the body is suppressed, causing it to be in a brief state of rest.