Effect of obstacle size and placement in 3D gravity-driven granular flow

Using LAMMPS, we simulate the effects of a stationary obstacle on the clogging probability of granular particles as they flow out of a 3D hopper.  Hopper clogging is a problem of great relevance to many industries that process powders.  The hopper is a cylinder with a conical base into which we place a spherical obstacle and pour spherical grains.  The opening at the base has a diameter small enough for the hopper to clog intermittently.  When particles flow out of the hopper, they are reintroduced at the top to ensure a continuous flow.  Each time the hopper clogs, particles at the bottom of the hopper are deleted and new particles reintroduced at the top.  We find that the number of particles that leave the hopper and the time between clogging events are affected by the size and position of the obstacle.  Our results indicate that, as long as the obstacle is not too close to the opening, the flow rate is not too sensitive to the presence of obstacles. For smaller obstacles, the probability of clogging goes down as the obstacle is moved closer to the opening, up to a point, whereas the clogging probability is less sensitive to the positioning of larger obstacles. Our simulation results are consistent with new experiments involving obstacles in 3D silos.