Effects of particle elongation on dense granular flows down a rough inclined plane

The mechanics of geophysical granular flow has been widely studied using spherical particles. However, natural granular materials are nearly always non-spherical, and a fundamental understanding of how particle shape affects the dynamics of granular flow remains elusive. Here, we use the discrete element method to simulate dense granular flows down a rough incline with systematically varied particle elongation (indicated by the length-to-diameter aspect ratio, AR). For each value of AR, we first determine the well-known h_stop curve delimiting no-flow and steady flow regimes and then carry out steady flow simulations above the h_stop curve to extract Pouliquen’s flow rule relations between the Froude number (Fr=u/(gh)^0.5) and the normalized flow thickness h/h_stop, where u is the mean flow velocity, h is the flow thickness and g is the gravitational acceleration. Our results show that the Fr-h/h_stop relations have a nonlinear dependence on AR (data collapse is not immediately achieved). Next, we analyze the statistics of particle orientation during the flow using a microscopic order parameter and find that more elongated particles tend to align better along a certain orientation, thus hindering the particle rotation. The dependence of the measured order parameter on AR seems to explain the trend in the Fr-h/h_stop relations, but further investigations are needed to quantitatively connect this micromechanical understanding with the macroscopic flow behaviors. Finally, the effects of other shape parameters, such as particle flatness and angularity, will be studied to draw a fuller picture of how the particle shape affects the mobility of geophysical granular flows.