Trewhela Tomás, Ancey Christophe
Laboratory of Environmental Hydraulics, École Polytechnique Fédérale de Lausanne, 1015 Écublens, Switzerland.
Exp Fluids. 2021;62(10):207. doi: 10.1007/s00348-021-03299-0. Epub 2021 Sep 25.
This paper shows how a conveyor belt setup can be used to study the dynamics of stationary granular flows. To visualise the flow within the granular bulk and, in particular, determine its composition and the velocity field, we used the refractive index matching (RIM) technique combined with particle tracking velocimetry and coarse-graining algorithms. Implementing RIM posed varied technical, design and construction difficulties. To test the experimental setup and go beyond a mere proof of concept, we carried out granular flow experiments involving monodisperse and bidisperse borosilicate glass beads. These flows resulted in stationary avalanches with distinct regions whose structures were classified as: (i) a convective-bulged front, (ii) a compact-layered tail and, between them, (iii) a breaking size-segregation wave structure. We found that the bulk strain rate, represented by its tensor invariants, varied significantly between the identified flow structures, and their values supported the observed avalanche characteristics. The flow velocity fields' interpolated profiles adjusted well to a Bagnold-like profile, although a considerable basal velocity slip was measured. We calculated a segregation flux using recent developments in particle-size segregation theory. Along with vertical velocity changes and high expansion rates, segregation fluxes were markedly higher at the avalanche's leading edge, suggesting a connection between flow rheology and grain segregation. The experimental conveyor belt's results showed the potential for further theoretical developments in rheology and segregation-coupled models.
本文展示了如何利用传送带装置来研究静止颗粒流的动力学。为了可视化颗粒体内部的流动，特别是确定其组成和速度场，我们使用了折射率匹配（RIM）技术，并结合粒子跟踪测速法和粗粒化算法。实施RIM带来了各种技术、设计和施工方面的困难。为了测试实验装置并超越单纯的概念验证，我们进行了涉及单分散和双分散硼硅酸盐玻璃珠的颗粒流实验。这些流动产生了具有不同区域的静止雪崩，其结构被分类为：（i）对流鼓起前沿，（ii）紧凑分层尾部，以及在它们之间的（iii）破碎粒度分离波结构。我们发现，由张量不变量表示的体应变率在识别出的流动结构之间有显著变化，其值支持了观察到的雪崩特征。尽管测量到相当大的底部速度滑移，但流速场的插值剖面与类似巴格诺尔德的剖面拟合得很好。我们利用粒度分离理论的最新进展计算了分离通量。除了垂直速度变化和高膨胀率外，分离通量在雪崩前沿明显更高，这表明流变学与颗粒分离之间存在联系。实验传送带的结果显示了流变学和分离耦合模型进一步理论发展的潜力。
