Bulbous head formation in bidisperse shallow granular flow over an inclined plane
Bulbous head formation in bidisperse shallow granular flow over an inclined plane
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DOI：
10.1017/jfm.2019.63
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发表时间：
2019-05-10
影响因子：
3.7
通讯作者：
Thornton, A. R.
中科院分区：
文献类型：
--
作者：
Denissen, I. F. C.;Weinhart, T.;Thornton, A. R.
在自然界中，斜坡上的快速浅层颗粒流经常以雪崩、滑坡和火山碎屑流的形式出现。在这些情况下，流动形成垂直于平面的反梯度（顶部大）颗粒尺寸分布。由于这种流动的表面速度大于平均速度，较大的材料被输送到流动前沿。这会导致下游方向的尺寸分离，导致由大颗粒组成的流动前沿。由于大颗粒通常比小颗粒摩擦力更大，流动前沿的流动性降低，导致所谓的球根状头部。这项研究的重点是这个球根状的头，我们发现出现在一个深度平均连续框架和离散粒子模拟的形成和演变。此外，我们的连续模型的数值解收敛到行波解，这使得一个非常有效的计算的长时间的流动行为。我们使用小规模的周期性离散粒子模拟来校准（关闭）我们的连续框架，并验证简单的一维（1-D）模型与全尺寸的3-D离散粒子模拟。比较表明，有条件下，该模型的工作令人惊讶的是，在强近似下，例如，瞬时垂直隔离。
Rapid shallow granular flows over inclined planes are often seen in nature in the form of avalanches, landslides and pyroclastic flows. In these situations the flow develops an inversely graded (large at the top) particle-size distribution perpendicular to the plane. As the surface velocity of such flows is larger than the mean velocity, the larger material is transported to the flow front. This causes size segregation in the downstream direction, resulting in a flow front composed of large particles. Since the large particles are often more frictional than the small, the mobility of the flow front is reduced, resulting in a so-called bulbous head. This study focuses on the formation and evolution of this bulbous head, which we show to emerge in both a depth-averaged continuum framework and discrete particle simulations. Furthermore, our numerical solutions of the continuum model converge to a travelling wave solution, which allows for a very efficient computation of the long-time behaviour of the flow. We use small-scale periodic discrete particle simulations to calibrate (close) our continuum framework, and validate the simple one-dimensional (1-D) model with full-scale 3-D discrete particle simulations. The comparison shows that there are conditions under which the model works surprisingly well given the strong approximations made; for example, instantaneous vertical segregation.