Computational investigation on bubble detachment from submerged orifice in quiescent liquid under normal and reduced gravity

Abstract

In this work numerical simulations have been carried out to study the problem of dynamic air bubble formation from a submerged orifice in quiescent liquid, under constant inflow condition, at normal and reduced gravity levels. A coupled level-set and volume-of-fluid method is used to simulate the bubble formation, bubble detachment, and the bubble rise above the orifice. For the described study, the authors have mainly focused on low and medium air flow rate for simulation of bubble formation at the orifice. The employed gravity levels g/g_e are in the range of 10⁰, 10⁻¹, and 10⁻². The influence of buoyancy on the bubble shape has been studied. The study includes the bubble volume, formation frequency, pinch-off rate, detached bubble diameter, and the bubble growth history for different air flow rates. Even for the static contact angle θ_s=0⁰, it is observed that at low gravity levels the bubble base spreads along the surface of the orifice plate away from the orifice rim during the expansion stage, and during the detachment stage the bubble base again comes back to the orifice rim. As the air flow rate is increased under normal and low gravity conditions, coalescence between the rising bubbles or between the detached bubble and the forming bubble at the orifice is observed. It is shown that the increasing trend of bubble size at detachment, with increasing air flow rate under normal gravity is reversed in the case of reduced gravity (g/g_e=10⁻²).