Discontinuous Shear Thickening (DST) fluids exhibit unique instability properties in a wide range of flow conditions. We present numerical simulations of a scalar model for DST fluids in a planar simple shear using the Smoothed Particle Hydrodynamics (SPH) approach. The model reproduces the spatially homogeneous instability mechanism based on the competition between the inertial and microstructural timescales, with good congruence to the theoretical predictions. Spatial inhomogeneities arising from a stress-splitting instability are rationalised within the context of local components of the microstructure evolution. Using this effect, the addition of non-locality in the model is found to produce an alternative mechanism of temporal instabilities, driven by the inhomogeneous pattern formation. The reported arrangement of the microstructure is generally in agreement with the experimental data on gradient pattern formation in DST. Simulations in a parameter space representative of realistic DST materials resulted in aperiodic oscillations in measured shear rate and stress, driven by formation of gap-spanning frictional structures.
Tuning the shear-thickening of suspensions through surface roughness and physico-chemical interactions
Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, MIT（麻省理工学院机械工程系哈特索普斯微流体实验室）；MultiScale Material Science for Energy and Environment, UMI 3466, CNRS-MIT（中法纳米研究中心能源与环境多尺度材料科学）；ENSL, CNRS, Laboratoire de physique（里昂高等师范学院法国国家科学研究中心物理实验室）
Emergence of transient reverse fingers during radial displacement of a shear-thickening fluid
玉米淀粉颗粒的高剪切浓水悬浮液表现出丰富的非线性流变特性。我们先前已经证明了当剪切稀化玉米淀粉悬浮液被牛顿流体置换时界面不稳定性的增长和开始，并且已经提出了使置换效率最大化的方法[Palak，R. Sathayanath，S. K. Kalpathy和R. Bandyopadhyay，胶体冲浪。物理化学。工程天冬氨酸，629（2021）127405]。在目前的工作中，我们探讨了在准二维径向Hele-Shaw细胞在其不连续的剪切增稠制度的致密的玉米淀粉水悬浮液的混溶位移。系统地研究了玉米淀粉悬浮液与水的内界面以及与空气的外界面的生长动力学。除了增长的界面不稳定性的内部接口，我们观察到一个短暂的撤回的悬浮液和指状不稳定性的形成在外部接口。我们证明，这些“反向指状”不稳定性是非常敏感的注入水的流速，间隙的Hele-Shaw细胞和浓度的取代玉米淀粉悬浮液，{和出现不考虑流体对之间的不可渗透性。我们认为，由于玉米淀粉悬浮液膨胀，由于高剪切速率所施加的驱替流体，外部悬浮液-空气界面的响应与回复力，导致空气渗透到悬浮液和反向手指的形成。我们注意到，反向指状物的生长显著降低了悬架的位移效率。最后，我们证明了在增长的内部和外部的界面图案的相关性，通过计算的速度，在封闭的稠密悬浮液中的应力传播。我们的研究结果是有用的，在理解流动的颗粒材料通过约束的几何形状，并可以扩展到研究应力传播的剪切增稠材料由于突…
