Gravity-Driven Flow and Clogging in the Presence of an Obstacle

We present experimental results of 2D gravity-driven flows of >10,000 monodisperse hard spheres (diameter = D) through an aperture (width = W). We introduce into the system a fixed obstacle of varying size (diameter = D₀) and distance above the aperture (L). We use a force sensor to measure the bulk flow rate, and high-speed, high-resolution video to track individual grains. We observe that obstacles tend to decrease the flow rate, but also decrease the clogging probability, and specifically measure the flow rate and clogging probability as a function of D₀ and L for different aperture widths. As our packing is crystalline, we can correlate these features with structural measurements in the material such as dislocations and the bond order parameter. We also present dynamical measurements such as nonaffine rearrangements and cooperative motion.