Numerical investigation on formation and motion of bubble or droplet in quiescent flow

Abstract

This paper describes the dynamic mechanisms of bubbles and droplets moving in quiescent flows. An improved diffuse interface method is adopted to capture the interfacial evolution of a two-phase flow, which can effectively suppress the phenomenon of interface dispersion. Preliminary simulations of a circular bubble/droplet moving from rest are first performed, and then, the interface shapes and vorticity distributions are compared to study the differences in the deformation mechanisms of bubbles and droplets. The processes of bubbles and droplets formed from a submerged orifice are, then, explored. The bubble formation process can be divided into nucleation, expansion, and detachment stages; for droplets, the characteristics of chaotic drip flow are considered. The interface shape and vorticity distribution of bubbles/droplets are analyzed, and the effects of the Weber number and Bond number on the detached bubble size and droplet flow regime are investigated. The effect of the contact angle on bubble formation is also examined. To reduce the detached bubble size, an improved method using an inserted orifice is proposed and confirmed. The inserted orifice is shown to have almost no effect on the formation of droplets, and the bubble/droplet formation and motion are independent of the inserted orifice length.