Fluid–structure interactions in underwater cylinder launch with high-pressure tail bubbles

This study presents an integrated experimental and numerical investigation of the interaction between a high-pressure tail bubble and a cylinder during underwater launch. The gas–liquid flow is modeled using the ideal gas law in conjunction with the boundary integral method, with particular emphasis on the effects of continuous gas release. A fluid–structure interaction model is developed to obtain the cylinder's acceleration. To validate the model, centimeter-scale experiments were conducted in a water tank, with the transient process captured using a high-speed camera. The numerical simulations accurately reproduce the experimental phenomena. A subsequent parametric study explores the dependence of tail bubble dynamics on key dimensionless parameters. The results demonstrate that sustained gas release can delay the collapse phase of the bubble. Regarding the pinch-off process, the evolution of the bubble's pinch-off radius follows a power-law of the scaling R¯∝τ¯α, where τ¯ is the time remaining until pinch-off, and the power-law exponent α varies with the Froude number. Three distinct pinch-off patterns are identified through hundreds of simulations: (i) bottom pinch-off, (ii) double pinch-off, and (iii) middle pinch-off. These regimes are organized into a phase diagram, with the double pinch-off serving as the transition boundary between the other two regimes in the Fr−ε parameter space. The location of this boundary is influenced by ambient pressure. The insights gained from this study provide a valuable reference for applications involving underwater launch dynamics.