A unified description of gravity- and kinematics-induced segregation forces in dense granular flows
A unified description of gravity- and kinematics-induced segregation forces in dense granular flows
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DOI：
10.1017/jfm.2021.688
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发表时间：
2021-08-26
影响因子：
3.7
通讯作者：
Umbanhowar, Paul B.
中科院分区：
文献类型：
--
作者：
Jing, Lu;Ottino, Julio M.;Umbanhowar, Paul B.
颗粒偏析在涉及流动颗粒材料的自然和工业过程中很常见。在不同的边界条件和作用力下，已经观察到复杂的、看似矛盾的偏析现象。通过离散元方法模拟，我们发现单粒子侵入者的偏析可以用统一的方式在不同的流动配置中描述。在重力和流动运动学独立变化的控制速度流中，通过测量作用于入侵粒子的力，得到了净偏析力的标度关系。标度律由两个附加项组成：类浮力重力压力梯度项和剪切速率梯度项，两者都依赖于粒径比。剪切速率梯度项反映了一种运动驱动机制，即较大（较小）的入侵者被推向较高（较低）剪切速率区域。在壁面驱动流动、斜壁面驱动流动、垂直筒仓流动和自由表面流动中验证了该模型的有效性，无需重新调整。将偏析力与闯入者的权重进行比较，得到了与各种流动构型下的实验和计算结果相匹配的偏析方向预测。
Particle segregation is common in natural and industrial processes involving flowing granular materials. Complex, and seemingly contradictory, segregation phenomena have been observed for different boundary conditions and forcing. Using discrete element method simulations, we show that segregation of a single particle intruder can be described in a unified manner across different flow configurations. A scaling relation for the net segregation force is obtained by measuring forces on an intruder particle in controlled-velocity flows where gravity and flow kinematics are varied independently. The scaling law consists of two additive terms: a buoyancy-like gravity-induced pressure gradient term and a shear rate gradient term, both of which depend on the particle size ratio. The shear rate gradient term reflects a kinematics-driven mechanism whereby larger (smaller) intruders are pushed toward higher (lower) shear rate regions. The scaling is validated, without refitting, in wall-driven flows, inclined wall-driven flows, vertical silo flows, and free-surface flows down inclines. Comparing the segregation force with the intruder weight results in predictions of the segregation direction that match experimental and computational results for various flow configurations.