Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Phys Rev E. 2019 Jul;100(1-1):012907. doi: 10.1103/PhysRevE.100.012907.
Granular materials immersed in a fluid are ubiquitous in daily life, industry, and nature. They include food processing, pastes, cosmetics, paints, concretes, cements, muds, wet sands, snows, landslides, and lava flow. They are known to exhibit a rich variety of complex rheological behavior, but the role of a fluid component in such behavior has remained poorly understood due to the nonlocal and many-body nature of hydrodynamic interactions between solid particles mediated by the fluid. We address this fundamental problem by comparing the microrheological response of athermal granular suspensions with and without hydrodynamic interactions to an externally driven probe particle by numerical simulations. We find that the presence of the fluid drastically increases the drag coefficient of the probe particle by more than one order of magnitude near the jamming transition. We reveal that this is a consequence of the nontrivial long-range nature of hydrodynamic interactions, which originates from unlimited cumulative transmission of near-field hydrodynamic interactions due to the incompressibility of both fluid and solid particles. Force chain formation of solid particles is dynamically coupled with hydrodynamic flow, leading to strong spatiotemporal fluctuations of flow pattern and nonlinear rheological response. Our study reveals essential roles of hydrodynamic interactions in complex rheological behavior of dense granular suspensions under an external drive.
浸没在流体中的颗粒材料在日常生活、工业和自然界中无处不在。它们包括食品加工、糊状物、化妆品、油漆、混凝土、水泥、泥浆、湿砂、雪、滑坡和熔岩流。众所周知，它们表现出丰富多样的复杂流变行为，但由于流体中介导的固体颗粒之间的流体动力相互作用具有非局部性和多体性，因此这种行为中流体成分的作用仍未被很好地理解。我们通过数值模拟比较了有和没有流体动力相互作用的非热颗粒悬浮液对外部驱动探针颗粒的微观流变响应，从而解决了这个基本问题。我们发现，在接近堵塞转变的情况下，流体的存在使探针颗粒的阻力系数急剧增加了一个数量级以上。我们揭示了这是由于流体动力相互作用的非平凡远程性质所致，这是由于流体和固体颗粒的不可压缩性导致近场流体动力相互作用的无限累积传递。固体颗粒的力链形成与流体流动动态耦合，导致流动模式和非线性流变响应的强时空波动。我们的研究揭示了在外部驱动下稠密颗粒悬浮液复杂流变行为中流体动力相互作用的重要作用。
