Title: Investigation of structure and dynamics of gravity driven dense granular flows with internal imaging

Author (Talk): Ashish Orpe, Clark University

Abstract:

We investigate the dynamics of dense granular flows during the drainage of a 3-dimensional silo filled with glass particles, and a liquid with the same refractive index. A plane of grains, away from the side walls is illuminated using a laser, and dark particles against a fluorescent background are imaged using a digital camera. The particle positions are identified and tracked over long durations to obtain flow characteristics such as mean squared displacements, velocity correlations and cage correlation functions. A hexagonal close packing is obtained near the walls while a random packing is obtained inside the silo. In the region spanning 10 particle diameters from the orifice, the velocity profile at a constant height across the cell is non-Gaussian and thus differing from a simple diffusing void model of silo flows. The distributions of the horizontal and vertical displacements for very short time scales show fat tails compared to a Gaussian indicating large fluctuations in particle displacements and possible cage breaking. The experimental results reveal a systematic effect of the side walls on the flow properties up to depths of 20 particle diameters. Furthermore, the observed flow behaviour is nearly flow-rate independent highlighting the importance of geometry.