利用LES -- DEM在水力和泥沙输运条件范围内自生沙丘中的颗粒动力学
Particle dynamics in self-generated dunes over a range of hydraulic and sediment transport conditions using LES--DEM
摘要：
在野外和实验室中，直接测量移动砂质底形上的垂直和纵向泥沙通量是极其困难的。在这项研究中，我们使用的LES-DEM（大涡模拟-离散元法）求解器SediFoam检查单个粒子的运动和产生的通量在一个域的自生沙丘。在SediFoam中，解决了沉积物颗粒的运动和碰撞以及它们与周围湍流的相互作用。数值模拟进行了一系列的运输设置，通过冲刷条件跨越床型成立，检查单个粒子的动力学。沙丘表面的时空演变进行了论证。自生沙丘在相对较低的雷诺数下是稳定的，但随后在较高的雷诺数下变得越来越不稳定;最终随着旁路颗粒和悬浮悬浮颗粒物数量的增加而被冲刷掉。从模拟的数据被用来检查颗粒的垂直夹带率和总泥沙负荷的分馏成床和悬浮分数作为运输条件的函数。研究还比较了输沙率使用床面形状的几何形状和celebrity的真实输沙率在不同的运输阶段。
英文摘要：
Direct measurement of vertical and longitudinal sediment fluxes on migrating sandy bedforms are extremely difficult to perform in both the field and laboratory. In this study we use the LES--DEM (large eddy simulation--discrete element method) solver SediFoam to examine the individual particle motions and resulting fluxes in a domain of self-generated dunes. In SediFoam, the motions of, and collisions among, the sediment grains as well as their interactions with surrounding turbulent flows are resolved. The numerical simulations are performed over a range of transport settings, spanning bedform inception through washout conditions, to examine the individual particle dynamics. The space-time evolution of dune surfaces is demonstrated. The self-generated dunes are stable at relatively low Reynolds numbers, but then become increasingly unstable at higher Reynolds numbers; eventually washing out as the number of bypass grains and particles in suspension increase. Data from the simulation are used to examine the vertical entrainment rate of particles and the fractionation of total sediment load into bed and suspended fractions as a function of transport conditions. The study also compares the sediment transport rate obtained using the bedform geometry and celerity to the true transport rate at different transport stages.
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