Abstract
We report simulations of a two-dimensional, dense, bidisperse system of
inelastic hard disks falling down a vertical tube under the influence of
gravity. We examine the approach to jamming as the average flow of particles
down the tube is slowed by making the outlet narrower. Defining coarse-grained
velocity and stress fields, we study two-point temporal and spatial correlation
functions of these fields in a region of the tube where the time-averaged
velocity is spatially uniform. We find that fluctuations in both velocity and
stress become increasingly correlated as the system approaches jamming. We
extract a growing length scale and time scale from these correlations.