Collapse dynamics and jet transition in the interaction between a near-wall cavitation bubble and a spherical air bubble

Investigating the interaction between a near-wall cavitation bubble and an adjacent air bubble holds significant value for elucidating the micro-mechanism of aeration in mitigating cavitation damage. The morphological evolution of the cavitation bubble and the underlying mechanisms of jet direction transition are explored using a three-phase compressible model. This model incorporates the effects of multi-phase fluid compressibility, heat and mass transfer, and surface tension. The results reveal that the liquid jet generated by the collapse of a cavitation bubble can be categorized into three Patterns: (1) a single jet directed toward the wall, primarily influenced by the solid boundary; (2) a reversed jet induced by the repelling effect of the air bubble; and (3) double jets formed under the combined influence of both the air bubble and the wall. The two critical δ-values distinguishing these patterns are ∼1.0 and 2.0. The dynamic behaviors of the near-wall cavitation bubble, with and without the presence of an air bubble, are thoroughly analyzed to better understand the associated physical processes. Compared to the collapse of a single cavitation bubble, the presence of an air bubble significantly suppresses bubble expansion and collapse intensity, leading to a marked reduction in jet velocity and peak wall pressure. The jet velocity in the presence of the air bubble is reduced to ∼13.9% of that observed without it at γ = 0.8. The inhibitory effect of the air bubble on the near-wall cavitation bubble is more pronounced with decreasing γ2 and diminishes with increasing γ.