Simulations of droplet merging with free surface and bubble column reactor with Finite-size Lagrangian particle tracking

In this work, we present the latest developments in the finite-size Lagrangian (FSL) tracking method we have recently proposed (Badreddine et al., 2015). The FSL method covers the situations in which dispersed-phase interfaces (bubbles or droplets) are larger than individual computational cells used in simulation, and thus not amenable by Lagrangian particle tracking (LPT). But in the same time, these interfaces are not large enough to be accurately simulated with interface tracking (IT) methods for a given mesh. The FSL method thus covers the middle ground between LPT and IT methods. It also inherits properties of the two; bubbles' shapes and sizes are prescribed with a phase indicator function and the continuous phase is resolved in Eulerian single-fluid framework as it would be in an IT method, and yet, the forces on individual bubbles are corrected from hydrodynamic force correlations used in LPT methods. After the initial phase of the FSL method verification, which was mainly focused on simulations of single moving bubbles, we now apply it to the real case of a square bubble column reactor, and compare time-averaged and fluctuation liquid velocity profiles against experiments. The distinct advantage of the FSL method, over the standard LPT, is the explicit resolution of turbulent structures, including the wakes behind individual bubbles. Bubble plume meandering was captured well in the simulations, as well as time-averaged vertical velocities. In addition, we broaden the class of multiphase situations we can deal with by coupling the FSL with an IT method. This extended methodology is demonstrated with cases of individual bubbles and droplets merging with a free surface.