D'Ortona Umberto, Thomas Nathalie, Zaman Zafir, Lueptow Richard M
Aix-Marseille Université, CNRS, Centrale Marseille, M2P2 UMR 7340, 13451 Marseille, France.
Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Dec;92(6):062202. doi: 10.1103/PhysRevE.92.062202. Epub 2015 Dec 4.
Walls in discrete element method simulations of granular flows are sometimes modeled as a closely packed monolayer of fixed particles, resulting in a rough wall rather than a geometrically smooth wall. An implicit assumption is that the resulting rough wall differs from a smooth wall only locally at the particle scale. Here we test this assumption by considering the impact of the wall roughness at the periphery of the flowing layer on the flow of monodisperse particles in a rotating spherical tumbler. We find that varying the wall roughness significantly alters average particle trajectories even far from the wall. Rough walls induce greater poleward axial drift of particles near the flowing layer surface but decrease the curvature of the trajectories. Increasing the volume fill level in the tumbler has little effect on the axial drift for rough walls but increases the drift while reducing curvature of the particle trajectories for smooth walls. The mechanism for these effects is related to the degree of local slip at the bounding wall, which alters the flowing layer thickness near the walls, affecting the particle trajectories even far from the walls near the equator of the tumbler. Thus, the proper choice of wall conditions is important in the accurate simulation of granular flows, even far from the bounding wall.
在颗粒流的离散元法模拟中，壁面有时被建模为紧密堆积的固定颗粒单层，从而形成粗糙壁面而非几何光滑壁面。一个隐含的假设是，由此产生的粗糙壁面与光滑壁面仅在颗粒尺度上局部不同。在这里，我们通过考虑流动层周边壁面粗糙度对旋转球形转筒中单分散颗粒流动的影响来检验这一假设。我们发现，改变壁面粗糙度会显著改变平均颗粒轨迹，即使在远离壁面的地方也是如此。粗糙壁面会导致流动层表面附近的颗粒向极地方向产生更大的轴向漂移，但会减小轨迹的曲率。增加转筒中的体积填充水平对粗糙壁面的轴向漂移影响不大，但会增加光滑壁面颗粒轨迹的漂移并减小其曲率。这些效应的机制与边界壁面处的局部滑移程度有关，局部滑移会改变壁面附近的流动层厚度，甚至影响远离转筒赤道附近壁面处的颗粒轨迹。因此，即使在远离边界壁面的情况下，正确选择壁面条件对于颗粒流的精确模拟也很重要。
