Influence of the impact angle on the motion and deposition of granular flows

The impact angle is an important but understudied factor that exerts a significant control on the propagation of granular flows. To investigate the influence of the impact angle on the motion and deposition of granular flows, flume experiments and numerical simulations were performed using impact angles ranging from 0° to 70°. Three-dimensional laser scanning and image analysis were employed to collect structural and kinetic information on these granular flows. Moreover, the evolution of the energy components of the granular flows was investigated at selected monitoring points and entire sliding mass using numerical simulations. A lower-velocity region in the middle portion of granular flows was observed in all cases. The area and shape of this region were found to be greatly influenced by the impact angle. An energy transfer from the middle and rear regions to the front of the granular flow was also observed, mediated by particle collisions. As a result, fluctuations in the velocity and energy of the particles in front region occurred, which in turn resulted in longer travel distance. The direction of movement and the travel distance changed when the granular flows encountered an obstacle along the horizontal chute. From the macroscopic point of view, the travel distance decreased as the impact angle increased. However, individual particles - especially in the front region - could travel longer distances even in the case of large impact angles owing to the collision-mediated energy transfer.