卡通沙丘的粒子动力学
Particle dynamics of a cartoon dune
摘要：
在一个狭窄的水流通道中，实验观察了沙漠沙丘缩小模型的时空演化。粒子跟踪法表明，模型沙丘的迁移速度比单个颗粒的迁移速度小一个数量级。特别是，侵蚀率由爬行（低能量）和跳跃（高能量）粒子的可比贡献。跃移流率略大，而跃移粒子数比蠕动粒子数少一个数量级。跃移颗粒的速度场与驱动流体的速度场具有可比性。可以观察到，剪应力的空间分布在沙丘顶部的上游达到最大值，而其最小值位于沙丘的下游脚。颗粒跟踪法表明，夹带颗粒的沉积主要发生在这两个极值之间的剪切应力的区域。此外，它表明，最初的三角形堆演变到一个稳定的状态，具有恒定的质量，形状，速度和包装分数后，一个周转时间已经过去了。在这段时间内，最初接触的颗粒之间的平均距离达到大约沙丘基本长度的四分之一。
英文摘要：
The spatio-temporal evolution of a downsized model for a desert dune is observed experimentally in a narrow water flow channel. A particle tracking method reveals that the migration speed of the model dune is one order of magnitude smaller than that of individual grains. In particular, the erosion rate consists of comparable contributions from creeping (low energy) and saltating (high energy) particles. The saltation flow rate is slightly larger, whereas the number of saltating particles is one order of magnitude lower than that of the creeping ones. The velocity field of the saltating particles is comparable to the velocity field of the driving fluid. It can be observed that the spatial profile of the shear stress reaches its maximum value upstream of the crest, while its minimum lies at the downstream foot of the dune. The particle tracking method reveals that the deposition of entrained particles occurs primarily in the region between these two extrema of the shear stress. Moreover, it is demonstrated that the initial triangular heap evolves to a steady state with constant mass, shape, velocity, and packing fraction after one turnover time has elapsed. Within that time the mean distance between particles initially in contact reaches a value of approximately one quarter of the dune basis length.
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