A numerical study of retracting thin gas films and their role in micro-bubble entrainment

Studying the mechanism of micro-bubble generation in air entrainment processes is important because of its role in numerous industrial and natural flows. These bubbles, ranging between 10-100 microns, can remain underwater for long times due to their low buoyancy and mass transfer rates. The exact mechanism of entrainment is unclear and quantitative information on bubble size distribution and dependence on flow parameters is very limited. Experimental evidence from drop-pool impact events has led researchers to hypothesize that impact events are the main contributor to the generation of micro-bubbles. Namely, in a phenomenon known as Mesler entrainment, very thin air films are entrapped between the pool and the impacting drop. These films have very high aspect ratios and after puncture, shed micro-bubbles while retracting on timescales much smaller than the outer flow timescales. Understanding the effects of such dynamics on micro-bubble entrainment has motivated us to numerically study this problem in 2D and 3D. Using a diffuse interface method, we perform two-phase simulations of retracting thin gas films in initially static liquid backgrounds to gain understanding and gather data that can be used in subgrid-scale modeling of micro-bubble generation.