A Numerical Study of Entrainment Mechanism in Axisymmetric Annular Gas-Liquid Flow

The main purpose of this study is to investigate liquid entrainment mechanisms of annular flow by computational fluid dynamics (CFD) techniques. In the modeling, a transient renormalization group (RNG) $k-ε$ model in conjunction with an enhanced wall treatment method was employed. In order to reconstruct the two-phase interface, the volume of fluid (VOF) geometric reconstruction scheme was adopted. Simulation results indicated that disturbance waves were generated first on the two-phase interface and that their evolution eventually resulted in the liquid entrainment phenomena. The most significant accomplishment of this work is that details of the entrainment mechanism are well described by the numerical simulation work. In addition, two new entrainment phenomena were presented. One entrainment phenomenon demonstrated that the evolution of individual waves caused the onset of liquid entrainment; the other one showed that the “coalescence” of two adjacent waves (during the course of their evolution) played an important role in the progression of liquid entrainment. Further analysis indicated that the two entrainment phenomena are inherently the same entrainment mechanism. The newly developed entrainment mechanism is based on conservation laws.