CFD modelling of gas entrainment at a propagating slug front

Slug flow is encountered frequently during multiphase fluid transport in pipes. The gas entrainment process at a slug front significantly affects the hydrodynamic behaviour of slug flows. Due to the complexity of the flow physics and the dynamic coupling of the affecting factors, the mechanism by which these factors contribute to the gas entrainment process is not clearly understood. Typical factors affecting the gas entrainment are pipe inclination, Taylor bubble propagation and liquid film. Current experiments are not able to clarify the effect of these factors on the flow characteristics of slugs. Hence, a computational fluid dynamics based numerical method is applied in this paper to simulate the gas entrainment process at the slug front. The objective is to investigate the factors affecting the gas entrainment. A 2D numerical model is created using a commercial CFD package Star-CCM+. To capture the dynamic behaviour of liquid-gas interface at the slug front, the volume of fluid (VOF) model with relatively fine mesh and small time step is used. The simulation results show that the turbulent kinetic energy at the slug front is closely related to the gas entrainment rate. The effects of pipe inclination, Taylor bubble propagation and liquid film flow parameters on the turbulent kinetic energy generation and gas entrainment process at the slug front are also discussed