Asymmetric collapse of double cavitation bubbles at oil–water interface and associated coupling effect

In multiphase flow applications such as pipeline transportation, the presence of oil–water interfaces and interactions between cavities jointly affect the collapse behavior of double bubbles. This study employs high-speed cameras to conduct an investigation into the pulsation characteristics of double cavitation bubbles near oil–water interfaces, focusing on the effects of the distance from the interface (γ), the distance between bubbles (λ), and the size ratio S. This study reveals that the enhancement effect of the interface on bubble re-expansion intensifies as the bubble approaches the oil–water interface. The primary Bjerknes forces acting on double bubbles are relatively weak; the resulting nonspherical deformation only becomes apparent after the bubble collapses, whereas the nonspherical deformation caused by the secondary Bjerknes forces becomes apparent during the bubble's first oscillation cycle. For equal size bubbles far from an interface, collapse occurs at the midpoint; near the interface, they migrate away from the interface. Unequal size double bubbles collapse asymmetrically, migrating toward the smaller one. At the end of the first oscillation cycle of the larger cavitation bubble, the ratio of the centroid migration displacements of each bubble pair exhibits an approximate inverse-square dependence on the initial size ratio S.