Study on multi-bubble coupling in underwater explosions under hypergravity conditions

The coupling mechanisms and morphological evolution characteristics of underwater multipoint explosion bubbles have long been a subject of extensive scientific interest due to their complex hydrodynamic behaviors and significant implications in both engineering and defense applications. Among various research methodologies, underwater explosion experiments conducted in centrifugal facilities—commonly referred to as hypergravity experiments—have emerged as one of the most effective approaches, primarily because of the simultaneous satisfaction of both the Mach number and the Froude number which are two critical dimensionless parameters governing dynamic similarity in fluid mechanics. This paper presents a comprehensive experimental and numerical investigation into the coupling dynamics of underwater multipoint explosion bubbles under hypergravity conditions. Specifically, a series of experiments were conducted under an accelerated gravitational field of 100g, enabling high-fidelity observation of the morphological evolution of dual explosion bubbles using high-speed imaging techniques. The captured visual data provided critical insights into bubble interaction processes and served as the foundation for the development and validation of a three-dimensional numerical model simulating underwater dual-bubble explosions in hypergravity environments.Through systematic comparison between experimental results and numerical simulations, the influence of gravitational intensity on the morphological evolution and characteristic parameters of coupled bubbles was thoroughly analyzed. It has been observed that under significantly elevated gravitational acceleration, the morphological evolution, pulsation dynamics, and migration characteristics of underwater explosion bubbles exhibit substantial deviations from those observed under normal gravity conditions. The hypergravity environment, as an extreme physical condition, intensifies both the pressure gradient within the surrounding fluid and the buoyancy forces acting on the bubble, thereby fundamentally altering the underlying hydrodynamic mechanisms. Specifically, the enhanced pressure gradient leads to a more pronounced asymmetry in the pressure distribution around the bubble interface, which in turn accelerates fluid motion and amplifies surface instabilities, resultting in faster and more violent bubble collapse phases, as well as stronger and more focused liquid jets during the rebound stage.Moreover, the increased gravitational acceleration significantly strengthens the buoyancy effect, which governs the direction and magnitude of bubble migration. Consequently, bubbles migrate more rapidly in the direction opposite to the effective gravity vector, and their trajectories become more predictable and less susceptible to small-scale perturbations. This enhanced migration velocity further influences the interaction intensity between multiple bubbles in a multipoint explosion scenario.The pulsation period of the bubble is also notably reduced under hypergravity, a phenomenon referred to as the "temporal compression" effect. Due to the increased restoring forces from both the ambient pressure and gravitational field, the bubble undergoes faster expansion and collapse cycles, resulting in a shorter overall lifetime and fewer oscillation periods. This spatiotemporal compression not only affects the phase relationship between coupled bubbles, thereby modifying their interference patterns and interaction intensity, but also redistribute the energy within the dual-bubble system, leading to distinct energy partitioning patterns compared to normal gravity scenarios.