Title: Descent of Single and Pairwise Intruders in Vibrated Gas-Fluidized Granular Materials

Author (Talk): Christopher Boyce, Columbia University

Abstract:

The descent of single and pairwise cylindrical intruders in a vibrated gas-fluidized granular media are investigated. Experiments are performed in a Hele-Shaw cell, and four intruder initial configurations are considered: a single intruder, two vertically aligned intruders, two horizontally aligned intruders, and two diagonally aligned intruders. The Reynolds number for the descent of the intruders (Rei) is 0.1 < Rei < 1. For all configurations, the intruders descend with an oscillatory descent velocity which is attributed to a variable particle packing through the height of the bed. The spatially-varying particle packing produces unconventional phenomena for the descent of objects such as larger intruders falling faster in certain regions of the bed, but slower in others. When two intruders are vertically aligned, the trailing intruder is observed catching up to the leading intruder, and the drafting-kissing-tumbling (DKT) phenomenon is observed. However, unlike the conventional DKT phenomenon where the trailing intruder leverages drag reduction to catch up to the leading intruder, here we observe that the leading intruder is halted until the trailing intruder catches up and displaces the leading intruder axially. We attribute this halting dynamic to the combined weight of the two intruders creating a denser particle packing below the leading intruder. The DKT phenomenon is even observed at long initial separation distances (4 intruder diameter). This work suggests that there are complex interactions occurring for the descent of single and pairwise objects in vibrated gas-fluidized granular media that have no analogy in Newtonian/non-Newtonian fluid dynamics or non-fluidized granular material.