Effect of fractal particle size distribution on the mobility of dry granular flows

This paper performs a numerical investigation on the kinetic behaviors of dry granular flows generated by the collapse of granular columns with different fractal particle size distributions (FPSDs) using the discrete element method. The FPSD has a remarkable impact on the regime and mobility of a granular flow. As the fractal dimension of a granular assembly increases, the translational velocities of the particles increase in the horizontal direction, whereas the rotational velocities decrease. The number of particles involved in the horizontal spreading increases due to the decreasing intensity of the contact shearing particle behavior. These increased translational velocities in the horizontal direction effectively facilitate particle spreading. A boundary layer is formed at the front bottom of the granular body in which the clockwise rotational velocities of particles are significantly increased, thereby benefiting particle spreading. The whole front of the granular flow obtains an immense spreading velocity. Moreover, the translational and rotational characteristics are dependent on the particle size. Smaller particles tend to translate and rotate faster than larger particles because of the greater particle contact forces of the former. As the fractal dimension increases, medium- and large-size particles obtain less kinetic energy than do small-size particles. Therefore, small-size particles play a crucial role in the mobility of granular flows in a granular assembly with a high fractal dimension.