Title: Structured Patterns in Granular Materials: From Bubble-Free to Bubbling Fluidization

Author (Table Talk): Javad Omidi, Columbia University

Abstract:

This study explores the formation of structured patterns in granular materials under two distinct fluidization regimes: bubble-free and bubbling. Through two-fluid model (TFM) simulations, we examine the emergence of Faraday waves in beds subjected to combined vertical and horizontal vibrations and the evolution of bubble structures driven by oscillatory gas injection. In the bubble-free regime, dimensional analysis yields regime maps, showing valuable insights into the behavior of the waves under varying conditions. The results showed that higher vertical vibration frequencies reduce horizontal mixing, while stronger horizontal vibrations enhance it. Increasing gas flow promotes vertical motion but suppresses lateral dispersion. In the bubbling regime, structured bubbling is induced by modulated gas injection at 7 Hz through segmented distributor plates. By varying the number (110) and phase offset (π/4 to π) of injection slices, we observe consistent changes in bubble size, vertical spacing, and spatial patterns. Notably, a phase offset of π/2 with 24 segments yields enhanced mixing while preserving ordered bubble lattices. These results offer a unified understanding of pattern formation in fluidized granular beds and demonstrate how external inputsvibrational or pneumaticcan be tuned to control transitions and optimize mixing.