Numerical investigation of particle saltation in the bed-load regime
Numerical investigation of particle saltation in the bed-load regime
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DOI：
10.1007/s11431-014-5606-1
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发表时间：
2014-08
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影响因子：
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通讯作者：
C. Ji;M. Ante;Avital Eldad;Dong Xu;W. John
中科院分区：
文献类型：
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作者：
C. Ji;M. Ante;Avital Eldad;Dong Xu;W. John
本文对湍流通道流中的颗粒跃迁进行了数值研究，该通道流具有由 2-3 层致密球体组成的粗糙床。在这项研究中，我们结合了三种最先进的技术，即湍流的直接数值模拟、颗粒变形、运动和碰撞的有限离散元组合建模以及流固相互作用的浸没边界法。在这里，我们通过将流量和粒子统计特征与已发布的数据进行比较来验证我们的代码，然后在典型的跳跃过程中呈现作用在粒子上的流体动力以及粒子坐标和速度。我们发现碰撞时颗粒流向速度的突然降低与垂直速度的增加之间存在很强的相关性，这表明大粒径颗粒的连续跃移是由颗粒入射角、局部粗糙床堆积排列和颗粒密度等碰撞参数控制的。这一物理过程与湍流相干结构起重要作用的颗粒夹带过程不同。给出了几个重要跳变参数的概率分布函数以及它们之间的关系。结果表明，撞击床颗粒迎风面的盐化颗粒比撞击背风面的盐化颗粒更有可能从粗糙的床面反弹。基于上述发现，提出了湍流通道流中大粒径颗粒的跳跃机制。
This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres. In this study, we combined three the state-of-the-art technologies, i.e., the direct numerical simulation of turbulent flow, the combined finite-discrete element modelling of the deformation, movement and collision of the particles, and the immersed boundary method for the fluid-solid interaction. Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities, during a typical saltation. We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision, which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle, local rough bed packing arrangement, and particle density, etc. This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role. Probability distribution functions of several important saltation parameters and the relationships between them are presented. The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside. Based on the above findings, saltation mechanisms of large grain-size particles in turbulent channel flow are presented.