3D jet impact and toroidal bubbles

A three-dimensional model of collapsing bubble with jet formation and impac t is presented in this paper. The strong instabilities of the jetting proce ss, impact, iind toroidal bubble rebound are dampened by a new smoothing sc heme based on least squares, thus enabling a smooth transition from a singl y connected bubble to a doubly connected toroidal bubble. A high order of m esh regularity is maintained by a mesh refinement procedure. The circulatio n of the How around the gaseous tube of the toroidal bubble is modelled by a generalization of the vortex ring method of Q. X. Wang et al. (Comput. Fl uids 25, 607 (1996)). Although our results indicate some differences from p revious axisymmetric results in terms of time to impact and fine features o f the evolving toroidal bubble profiles, the essential physics associated w ith the jet impact. such as the circulation around the torus and the reboun d of the toroidal bubble, are well captured in the new model. We also prese nt, for the first time, results for fully three-dimensional bubbles in whic h buoyancy effects lead to oblique jetting. (C) 2001 Academic Press.