Numerical investigation on influences of injection flow rate on bubbling flow at submerged orifices

Abstract

In this study, we numerically investigated the formation of bubbles by gas injection through an orifice in a stagnant liquid column and the flow field surrounding the bubbles after detachment under several flow conditions. To this end, we employed an enhanced coupling method that combines the advantages of mass conservation property of the volume-of-fluid (VOF) method with the boundedness and continuity of a conservative level-set (LS) function for multiphase computations to achieve a smoothened and sharpened interface. The coupling method was integrated into an incompressible Navier–Stokes solver to investigate the bubbling flow under various injection conditions. The simulated results were first validated against the experimental data of a benchmark test case to assess its reliability. The capability of the solver was also confirmed by examining the computed results and comparing them with those of the other studies. Subsequently, we simulated bubbling flow under different injected gas conditions and several orifice radii. The simulated results indicated that at low gas injection flow rates, the detachment time of bubbles, pinched off the orifice rim, could be predicted depending on the orifice radius and volume flow rate of the gas, whereas orifice radius had a notable influence on the detached volume of bubbles. In addition, the gas injection flow rate had a significant influence on the pressure field surrounding the bubbles after detachment, which is useful for studying of the bubbling flows and for the optimal design of small-scale systems.