Lagrangian Particle Statistics in a Homogeneous Swarm of Air Bubbles Rising in a Vertical Channel

Multiphase turbulent flows involving mixtures of water, oil, and gas are ubiquitous in nature and in industrial processes. In systems utilizing multiphase flows for rapid mixing, it is necessary to predict the dilution and dispersion of passive tracers to assess the performance of the system. Using a set of direct numerical simulations (DNS) of a homogeneous air bubble swarm rising in a vertical channel, we attempted to test the validity of (1) G.I. Taylor’s 1921 turbulent diffusion law, and (2) particle-pair statistics as pertained to Richardson’s 1926 4/3th dispersion law in bubbly flows. The air void fraction in the simulations was fixed at 0.5% and we considered two scenarios – a monodispersed bubble swarm with 2mm-diameter bubbles and a bi-dispersed swarm with 2mm- and 4mm-diameter bubbles. We will compare our results to those from homogeneous isotropic turbulence (HIT), highlight the differences observed, and propose ideas to improve on existing turbulent diffusion theories.