Dynamic Interactions of Large-Scale Tandem Bubbles with a Rigid Wall

Abstract

In natural phenomena and industrial applications, bubble evolution is often governed by complex inter-bubble interactions and boundary effects. However, the evolution of tandem bubbles near boundaries has not been thoroughly investigated in existing studies. The interface-sharpening six-equation multiphase model is capable of accurately capturing rapid topology evolution at gas–liquid interfaces, enabling the prediction of complex phenomena such as bubble coalescence and collapse. In this study, the accuracy of the numerical model is validated through free-field experiment and the unified bubble theory. The numerical model simulates the evolution of single bubbles, tandem bubbles, and out-of-phase tandem bubbles near a rigid wall. The effects of inter-bubble distance (γ_bb ∈ [0.5, 1.6]) and out-of-phase parameter (τ ∈ [0, 1]) on bubble dynamics and wall impact are investigated, with particular attention to their influence on bubble penetration. The impact load on the wall is primarily composed of bubble collapse pressure, water-jet impact pressure, and bubble pulsation pressure. As γ_bb increases, the collapse mechanism of upper bubble transitions from water-jet induced mechanism to a local high-pressure induced mechanism, reaching the highest impact intensity at γ_bb = 1.2. As τ increases, the collapse mechanism of upper bubble gradually shifts from low-pressure bubble suppression mechanism to a local high-pressure induced mechanism. When γ_bb ≤ 0.9, the impact enhancement effect on the wall can be induced by adjusting the parameter τ, with the optimal impact enhancement occurring at τ = 0.833. These transitions in collapse mechanisms are further explained by the Kelvin impulse theory. The analytical conclusions provide valuable insights into the complex evolution of tandem bubbles near boundaries.