Dynamics of re-entrant jets during the Rayleigh collapse of gas bubbles near an interface*

When a cavitation bubble collapses near an interface (e.g., another bubble, a rigid object, a free surface), the subsequent collapse is often non-spherical. During the collapse, rarefaction/compression waves are produced, which interact with the original bubble and communicate the presence of the interface. These effects break the symmetry of the bubble collapse and lead to the formation of re-entrant jets. However, jet dynamics are not fully understood. In the present work, to describe a wide spectrum of jet formation, different kinds of interface are positioned near a primary bubble, whose jet dynamics are under consideration. The 3D compressible Navier-Stokes equations for multiphase flows are solved numerically using a solution-adaptive high-order accurate method. Here, dynamics of re-entrant jets are illustrated by jet velocity and strength in terms of driving pressure and initial distance between the primary bubble and secondary interface. Specifically, varying driving pressure and size ratio of the bubble and interface can change the effect of secondary interface, and subsequently increase/decrease the jet velocity and strength. Different regimes are established to classify different jet types.