Investigating the rheology of fluidized and non-fluidized gas-particle beds: implications for the dynamics of geophysical flows and substrate entrainment
Investigating the rheology of fluidized and non-fluidized gas-particle beds: implications for the dynamics of geophysical flows and substrate entrainment
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DOI：
10.1007/s10035-021-01192-5
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发表时间：
2022-02-01
期刊：
影响因子：
2.4
通讯作者：
Jean-Francois, Dietiker
中科院分区：
文献类型：
--
作者：
Eric, Breard C. P.;Luke, Fullard;Jean-Francois, Dietiker
自然地球物理质量流是最复杂的颗粒系统之一，其动力学经常被间隙流体的存在所改变。要预测它们的跳动，需要开发模型来估计这些危险洋流中的固体应力，在这些洋流中可能会产生过大的孔隙流体压力。采用离散元模拟(DEM-CFD)和粗粒化后处理技术(CG)，研究了水平和倾斜平面上非定常气固两相流态化颗粒床的流变性。与浸没在粘性流体中的床层相似，空气床层的有效摩擦系数可以定义为经典的Mu(I)流变学和无量纲流体或固体压力的函数，以解释倾斜上具有超孔压的颗粒流的失效和动力学。然而，在气固两相床中，由于流体的阻力和颗粒的碰撞而产生的膨胀会使其有效摩擦性能发生很大的变化。与水-颗粒流动中颗粒温度可以忽略不计的常见假设相反，在我们的气固两相模拟中，速度涨落对应力张量的贡献是显著的。因此，即使当流体在惯性区完全流态化时，剪应力也不为零。这些结果表明，有必要更好地了解速度波动，以预测剪切流态化混合物的有效粘度，并与许多应用相关。值得注意的是，统一的方法对于在单一流动中包含一系列流态化条件的许多地球物理流动是有用的，例如火山碎屑密度流和雪崩。
Natural geophysical mass flows are among the most complex granular systems and their dynamics are often modified by the presence of an interstitial fluid. Prediction of their runout requires the development of models estimating the solid stresses in these hazardous currents wherein excess pore-fluid pressure can develop. We use discrete element modelling (DEM-CFD) with a Coarse-Graining post-processing technique (CG) to investigate the rheology of unsteady gas-particle fluidized to non-fluidized granular beds placed on horizontal and inclined planes. Similar to fluidized beds immersed in viscous fluids, the effective friction coefficient of air-fluidized beds can be defined as a function of the classic mu(I)-rheology and the non-dimensional fluid or solid pressure to explain the failure and dynamics of granular flows with excess pore pressure on inclines. However, dilation imposed by fluid drag and particle collisions in gas-particle fluidized beds can drastically change its effective frictional properties. In contrast with the common assumption in water-particle flows that granular temperature is negligible, in our gas-particle simulations, the contribution of the velocity fluctuations to the stress tensor is significant. Hence, the shear stress is found to be non-zero even when the flow is fully fluidized in the inertial regime. These results suggest the need to better understand velocity fluctuations to predict the effective viscosity of sheared fluidized mixtures and are relevant for many applications. Notably, a unified approach is useful for many geophysical flows that encompass a range of fluidization conditions in a single flow such as pyroclastic density currents and snow avalanches.