Bubbling and mixing of vibrated and non-vibrated gas-fluidized active granular matter

Abstract

Numerical simulations are used to study the effect of varying magnitudes of active matter force on non-vibrated and vertically vibrated gas-fluidized granular materials. We observe that if the ratio of active matter force to gravity is less than 1, but above 0, gas bubbles produced by fluidization generally increase in size which promotes mixing. However, if the ratio of active matter force to gravity exceeds 1, then the active matter force suppresses bubbling and the mixing is poorer. Furthermore, we find that if the active matter force significantly exceeds 1, the mixing can be enhanced despite no bubbling, owing to diffusion. By vertically vibrating the granular bed, and subsequently producing structured bubbling, we find that bubbles persist for larger active matter force, which we attribute to the larger bubble size observed for structured bubbling as compared to chaotic bubbling. Finally, we present a non-dimensional regime map describing the transition of sub-diffusive, diffusive, and advective transport regimes depending on the balance of active matter force to drag force to gravitational force for fluidized active granular materials.