Modeling tail bubble dynamics during the launch of an underwater vehicle using the boundary element method

A tail bubble is generated behind a high-speed vehicle at the early stage of the underwater launch process. The tail bubble dynamic behavior involves expansion, overexpansion, contraction, pinch-off and jet formation, and it significantly influences the vehicle's movement. However, the tail bubble dynamic behavior is an issue not very well studied. This paper establishes a numerical model for the interaction between the tail bubble and the vehicle based on the boundary element method (BEM) to gain new insight into this issue. The BEM results are compared to a computational fluid dynamics model to validate the numerical model, and good agreement is achieved. Additionally, a convergence test of the BEM model is conducted to verify its independence of the mesh size. The influence of some governing parameters on the evolution of the tail bubble is then systematically studied, focusing on its maximum radius, pinch-off time, and pinch-off position. There are two pinch-off position regimes of the tail bubble, one at the bottom and the other near the middle.