Discrete and continuum modelling of grain size segregation during bedload transport
Discrete and continuum modelling of grain size segregation during bedload transport
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DOI：
10.1017/jfm.2020.274
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发表时间：
2020-05
影响因子：
3.7
通讯作者：
R. Chassagne;R. Maurin;J. Chauchat;John Gray;P. Frey
中科院分区：
文献类型：
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作者：
R. Chassagne;R. Maurin;J. Chauchat;John Gray;P. Frey
颗粒尺度的离散元模拟双分散混合物在推移质输送过程中被用来理解和模拟颗粒介质中的推移质输送和颗粒尺寸分离。对于粗颗粒床层顶部的初始细颗粒分布，本文研究了重力驱动的细颗粒向下进入床层准静态部分的渗流/分离。观察到偏析是由细粒层底部的惯性数驱动的，而与细粒数无关。利用Thornton，Gray&Hogg(流体力学杂志，第550卷，2006年，第1-25页)和Gray&Chugunov(流体机械杂志，第569卷，2006，第365-398页)的连续介质颗粒尺寸分离模型，构建了一种新的浓度分布的行波解。观察到的行为与浓度和惯性数的影响之间的局部平衡有关。精确解的存在取决于偏析通量和扩散系数对惯性数的相同依赖关系。这种函数依赖性使得连续介质模型能够定量地再现离散模拟。这些结果极大地改善了我们对粒度分离动力学的理解，代表了在湍流推移质输运背景下多分散颗粒流的放大过程向前迈进了一步。
Grain-scale discrete element simulations of bidisperse mixtures during bedload transport are used to understand, and model, bedload transport and particle-size segregation in granular media. For an initial distribution of fine particles on top of a coarse granular bed, this paper investigates the gravity driven percolation/segregation of the fine particles down into the quasi-static part of the bed. The segregation is observed to be driven by the inertial number at the bottom of the fine particle layer, and is independent of the number of fine particles. A novel travelling wave solution for the evolving concentration distribution is constructed using the continuum particle-size segregation model of Thornton, Gray & Hogg (J. Fluid Mech., vol. 550, 2006, pp. 1–25) and Gray & Chugunov (J. Fluid Mech., vol. 569, 2006, pp. 365–398). The observed behaviour is shown to be related to a local equilibrium between the influence of the concentration and of the inertial number. The existence of the exact solution relies on the segregation flux and the diffusion coefficient having the same dependency on the inertial number. This functional dependence allows the continuum model to quantitatively reproduce the discrete simulations. These results significantly improve on our understanding of the size segregation dynamics and represent a step forward in the up-scaling process to polydisperse granular flows in the context of turbulent bedload transport.