Thorens Louison, Måløy Knut J, Flekkøy Eirik G, Sandnes Bjørnar, Bourgoin Mickaël, Santucci Stéphane
ENSL, CNRS, Laboratoire de Physique, F-69342 Lyon, France.
PoreLab, The Njord Centre, Department of Physics, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway.
Soft Matter. 2023 Dec 13;19(48):9369-9378. doi: 10.1039/d3sm00717k.
Numerous natural and industrial processes involve the mixed displacement of liquids, gases and granular materials through confining structures. However, understanding such three-phase flows remains a formidable challenge, despite their tremendous economic and environmental impact. To unveil the complex interplay of capillary and granular stresses in such flows, we consider here a model configuration where a frictional fluid (an immersed sedimented granular layer) is slowly drained out of a horizontal capillary. Analyzing how liquid/air menisci displace particles from such granular beds, we reveal various drainage patterns, notably the periodic formation of dunes, analogous to road washboard instability. Considering the competitive role of friction and capillarity, a 2D theoretical approach supported by numerical simulations of a meniscus bulldozing a front of particles provides quantitative criteria for the emergence of those dunes. A key element is the strong increase of the frictional forces, as the bulldozed particles accumulate and bend the meniscus horizontally. Interestingly, this frictional enhancement with the attack angle is also crucial in small-legged animals' locomotion over granular media.
许多自然和工业过程都涉及液体、气体和颗粒物质通过限制结构的混合驱替。然而，尽管三相流具有巨大的经济和环境影响，但理解此类三相流仍然是一项艰巨的挑战。为了揭示此类流动中毛细管应力和颗粒应力的复杂相互作用，我们在此考虑一种模型配置，即一种摩擦流体（浸没的沉积颗粒层）从水平毛细管中缓慢排出。通过分析液/气弯月面如何从此类颗粒床中驱替颗粒，我们揭示了各种排水模式，特别是沙丘的周期性形成，类似于路面搓板状失稳。考虑到摩擦力和毛细作用的竞争作用，一种由弯月面推挤颗粒前沿的数值模拟支持的二维理论方法为这些沙丘的出现提供了定量标准。一个关键因素是，随着被推挤的颗粒堆积并使弯月面水平弯曲，摩擦力会大幅增加。有趣的是，这种随攻角增加的摩擦增强在小型有腿动物在颗粒介质上的运动中也至关重要。
