A numerical study of oscillation induced coalescence in bubbly flows

Direct numerical simulations of two-way oscillating bubbly flows in a domain bounded by solid walls are presented. Ignoring gravity, the two- and three-dimensional flows of equal-sized bubbles are driven by periodically oscillating pressure gradients in the X and Z directions with the same amplitude and frequency but different phases. The results show that the oscillations will drive the bubbles together, promoting coalescence. The results depend on the amplitude and frequency, resulting in “crawling” flow, “revolving” flow, and “oscillating” flow. As the amplitude increases, the critical frequency separating these three flow regions increases. For each amplitude, there is an optimum frequency near the transition region between the crawling flow and the revolving flow that yields the fastest coalescence. A qualitative comparison between two- and three-dimensional flows shows that the dynamics observed for the two-dimensional flows is also found in three-dimensions.