Numerical simulation of the motion and interaction of bubble pair rising in a quiescent liquid

Abstract

In the present study, the motion and interaction of a bubble pair rising in a stationary liquid are simulated in two dimensions using the volume of fluid method (VOF) in the open-source CFD package OpenFOAM. For validation, the single bubble rising for different regimes was simulated. Comparing the present study results and previous numerical and experimental results showed that the results have a good agreement. In the present study, the bubble pair is arranged along a horizontal line, and results showed that in 2D domain four different interactions happen between the bubble pair rising based on the Bond (Bo) and Morton (Mo) numbers which are: coalescence, bouncing, zigzagging, and breakup. The simulations are done at three different slopes of the line connecting the center of two bubbles (θ=[0°, 45°, and 90°]), which shows the different arrangements of bubble pairs. At θ=90°, due to the attraction created by the wake of the leading bubble, the trailing bubble gets a significant acceleration in its motion, and will coalesce in the absence of surfactants. The results showed that the value of the trailing bubble velocity increases with decreasing the separation distance between the bubbles. Also, the rising velocity of the trailing bubble is always greater than the velocity of a single bubble due to the attraction effect of the leading bubble’s wake. The drag force of a trailing bubble decreases with decreasing the separation distance between the bubbles. Finally, a general criterion based on dimensionless numbers of Bo and Mo is presented to determine the type of interaction between bubble pair.