粗糙壁面和光滑壁面对转鼓内宏观流动的影响
Influence of Rough and Smooth Walls on Macroscale Flows in Tumblers
摘要：
在离散元方法模拟颗粒流的壁有时被建模为一个紧密堆积的单层固定颗粒，导致粗糙的壁，而不是一个几何光滑的壁。一个隐含的假设是，所得到的粗糙壁与光滑壁仅在粒子尺度上局部不同。在这里，我们测试这一假设，考虑壁粗糙度的影响，在周边的流动层上的流动的单分散颗粒在一个旋转的球形颗粒。我们发现，不同的壁粗糙度显着改变平均粒子的轨迹，甚至远离壁。粗糙壁面引起流动层表面附近颗粒更大的极向轴向漂移，但减小了轨迹的曲率。对于粗糙壁，增加颗粒填充水平对轴向漂移的影响很小，但对于光滑壁，增加漂移同时减少颗粒轨迹的曲率。这些效应的机制与边界壁处的局部滑移程度有关，这改变了壁附近的流动层厚度，甚至影响了远离赤道附近壁的颗粒轨迹。因此，正确选择壁面条件对精确模拟颗粒流是很重要的，即使远离边界壁面也是如此。
英文摘要：
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.
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