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A Taylor vortex analogy in granular flows

机译:颗粒流中的泰勒涡旋比喻

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Fluids sheared between concentric rotating cylinders undergo a series of three-dimensional instabilities. Since Taylor's archetypal 1923 study(1), these have proved pivotal to understanding how fluid flows become unstable and eventually undergo transitions to chaotic or turbulent states(2-5). In contrast, predicting the dynamics of granular systems - from nano-sized particles to debris flows - is far less reliable. Under shear these materials resemble fluids, but solid-like responses, non-equilibrium structures and segregation patterns develop unexpectedly(6-9). As a result, the analysis of geophysical events(10) and the performance of largely empirical particle technologies might suffer(11,12). Here, using gas fluidization to overcome jamming(6,13), we show experimentally that granular materials develop vortices consistent with the primary Taylor instability in fluids. However, the vortices observed in our fluidized granular bed are unlike those in fluids in that they are accompanied by novel mixing segregation transitions. The vortices seem to alleviate increased strain by spawning new vortices, directly modifying the scale of kinetic interactions. Our observations provide insights into the mechanisms of shear transmission by particles and their consequent convective mixing.
机译:在同心旋转圆柱体之间剪切的流体经历了一系列三维不稳定性。自从泰勒(Taylor)在1923年进行的原型研究(1)以来,已证明这些对于理解流体如何变得不稳定并最终转变为混沌或湍流状态至关重要(2-5)。相反,预测颗粒系统的动力学-从纳米级颗粒到泥石流-远不那么可靠。在剪切作用下,这些材料类似于流体,但是类似固体的响应,非平衡结构和偏析模式出乎意料地发展(6-9)。结果,对地球物理事件的分析(10)和很大程度上基于经验的粒子技术的性能可能会受到影响(11,12)。在这里,使用气体流化技术克服了堵塞现象(6,13),我们通过实验证明了颗粒状物质会形成与流体中主要的泰勒不稳定性相一致的旋涡。但是,在我们的流化颗粒床中观察到的涡流与流体中的涡流不同,因为它们伴随着新的混合偏析过渡。涡流似乎通过产生新的涡流来减轻应力的增加,直接改变了动力学相互作用的规模。我们的观察结果提供了有关颗粒的剪切传递机理及其对流混合的见解。

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