粗糙壁面和光滑壁面对宏观颗粒偏析的影响
Influence of Rough and Smooth Walls on Macroscale Granular Segregation Patterns
摘要：
大小双分散颗粒材料在一个球形的结晶器分离成两种不同的模式的三个带，要么小颗粒在赤道和大颗粒在两极或反之亦然，这取决于在结晶器的填充水平。在这里，我们使用离散元方法（DEM）模拟与支持定性实验，探索隔离模式上的隔离壁粗糙度的效果，建模的隔离壁作为一个紧密堆积的单层的固定颗粒导致粗糙的墙壁，或作为一个几何光滑的墙壁。尽管湍流壁仅在其外围与流动层接触，但壁面粗糙度的影响是深远的。光滑的壁倾向于一个小-大-小（SLS）带模式在极点-赤道-极点，但最高的填充分数;粗糙的壁倾向于一个大-小-大（LSL）带模式在所有，但最低的填充分数。这是因为光滑的壁诱导小颗粒的极向轴向漂移和大颗粒的赤道方向漂移，导致SLS带图案。另一方面，粗糙的壁导致两种尺寸的颗粒在流的表面处向极移动，但是由于径向偏析，小颗粒在流动层中渗透较低，在流动层中存在朝向赤道的返回漂移，而大颗粒留在极附近的表面处，导致LSL带图案。倾向于两个带模式中的任何一个取决于填充水平的岩石和岩石的边界壁的粗糙度。
英文摘要：
Size bidisperse granular materials in a spherical tumbler segregate into two different patterns of three bands with either small particles at the equator and large particles at the poles or vice versa, depending upon the fill level in the tumbler. Here we use discrete element method (DEM) simulations with supporting qualitative experiments to explore the effect of the tumbler wall roughness on the segregation pattern, modeling the tumbler walls as either a closely packed monolayer of fixed particles resulting in a rough wall, or as a geometrically smooth wall. Even though the tumbler wall is in contact with the flowing layer only at its periphery, the impact of wall roughness is profound. Smooth walls tend toward a small-large-small (SLS) band pattern at the pole-equator-pole at all but the highest fill fractions; rough walls tend toward a large-small-large (LSL) band pattern at all but the lowest fill fractions. This comes about because smooth walls induce poleward axial drift of small particles and an equator-directed drift for large particles, resulting in an SLS band pattern. On the other hand, rough walls result in both sizes of particles moving poleward at the surface of the flow, but due to radial segregation, small particles percolate lower in the flowing layer where there is a return drift toward the equator while large particles remain at the surface near the pole, resulting in an LSL band pattern. The tendency toward either of the two band patterns depends on the fill level in the tumbler and the roughness of the tumbler's bounding wall.
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