Crown control in a pair of cavitation bubbles close to a free surface: A numerical study

When a cavitation bubble re-expands near the surface of a liquid, an axisymmetric crown forms around the jet that is initially produced. Controlling this crown is essential if the first jet is to be used in engineering applications such as laser-induced transfer (LIT). Herein, we introduce a second cavitation bubble to control the formation and growth of the crown. Numerical simulations were performed using the compressibleInterIsoFoam solver within the open-source platform OpenFOAM, incorporating a geometric volume-of-fluid approach for tracking interfaces. Detailed analysis showed that a reversal in curvature across the concave interface indicates the moment of crown formation, and this is induced by flow focusing during bubble contraction or momentum transfer from a second expansion. In the presence of the second bubble, the crown type can be classified as either enhanced or inhibited in comparison with a single-bubble scenario. The velocity of crown formation, vcf, is defined to describe the crown type, and a parametric study of crown types was conducted based on the dimensionless stand-off distances, gamma 1 and gamma 2. The findings of this study offer new insights into the field of LIT.