Goldfarb David J, Glasser Benjamin J, Shinbrot Troy
Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, New Jersey 08854-8058, USA.
Nature. 2002 Jan 17;415(6869):302-5. doi: 10.1038/415302a.
Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows.
不稳定波在流体剪切层中已被长期研究。这些波除了影响船舶、飞机和传热装置后方的滑流稳定性外，还会影响大气和海洋中的输运。尽管颗粒流在地球物理和工业系统中很重要，但此前尚未有关于其相应不稳定性的记录。在此，我们报告在分流板下游倾斜平面上流动的两股相同颗粒流之间的界面处会形成破碎波。剪切速率或倾斜角度的变化会导致此类波突然出现。我们分析了一个与实验数据定性相符的颗粒流模型；该模型表明，这些波是由流动颗粒床中剪切应变和拉伸应变之间的竞争导致的。我们提出了一个无量纲剪切数，它控制着稳定流和波动流之间的转变。
