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.

中文翻译：

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静态流动中气泡或液滴形成与运动的数值研究

本文描述了气泡和液滴在静态流中运动的动力学机制。采用一种改进的扩散界面方法来捕获两相流的界面演化，可以有效地抑制界面分散现象。首先对圆形气泡/液滴从静止状态运动进行了初步模拟，然后比较了界面形状和涡度分布，以研究气泡和液滴变形机制的差异。然后，研究了由浸没孔口形成的气泡和液滴的过程。气泡的形成过程可分为成核，膨胀和分离阶段。对于液滴，考虑了混沌滴流的特性。分析气泡/液滴的界面形状和涡度分布，并研究了韦伯数和键数对分离的气泡尺寸和液滴流态的影响。还检查了接触角对气泡形成的影响。为了减小气泡的分离尺寸，提出并证实了使用插入孔口的改进方法。示出了插入的孔口对液滴的形成几乎没有影响，并且气泡/液滴的形成和运动与插入的孔口长度无关。