Predictability and benefits of coupled Eulerian-Lagrangian approach over Eulerian characterization of droplet annular flow

Wavy annular flow and subsequent droplet dispersion in air-water two-phase flow has been studied numerically using conventional Eulerian volume of fluid (VOF) solver and coupled Eulerian-Lagrangian approach. The VOF based investigation has been reported to highlights the formation of droplet swarm and its population dynamics. Coupled Eulerian-Lagrangian method has also been shown to replicate similar features with lesser computational effort. Entrainment, deposition, fragmentation and unification are traced from the numerical simulation, which ultimately predicts the volume filling behavior of the droplets inside the tube. Flow kinematics around droplet is critically assessed numerically for finding out reasons behind deposition, fragmentation and unification. A comparative behavior between different velocity ratios of gas and liquid flow rates are presented which clearly shows higher entrainment rate as shear between annular liquid and gaseous core increases. An assessment of the droplet population in coupled Eulerian-Lagrangian method shows the generation of the smaller sized spherical droplet by entrainment and fragmentation route.