Mechanism study of bubble dynamics under the buoyancy effects

The motion of a single bubble in a 2-D vertical channel filled with stagnant or moving fluid is simulated for various sets of conditions using the computational fluid dynamics(CFD) method. The volume of fluid (VOF) model is applied to track the interface of the bubble. Corresponding results are compared with experimental and theoretical studies, and good agreement is achieved. Two-phase flows composed of various fluids are simulated to check the impact of physical properties on bubble dynamics, and buoyancy is found to have a key influence on the bubble rising behavior, including both the trajectory and the terminal rising velocity. The dimensionless number Bu is introduced to characterize this effect, and a larger Bu leads to a larger bubble rising velocity. Three other dimensionless numbers Eo, We, and Mo are introduced to study the bubble deformation which can be characterized by aspect ratio E, and an approximately linear relationship is found between E, Eo, and bubble size. Inertial force is proved to influence the bubble motion significantly in moving fluid, whose velocity dominates the bubble terminal speed. The simulation of motion for two bubbles is also performed and investigated detailedly.