Shear-Driven Flow of Athermal, Frictionless, Spherocylinder Suspensions in Two Dimensions: Orientational Ordering and Spatial Correlations
Shear-Driven Flow of Athermal, Frictionless, Spherocylinder Suspensions in Two Dimensions: Orientational Ordering and Spatial Correlations
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二维无热、无摩擦、球柱悬浮液的剪切驱动流动：方向排序和空间相关性
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发表时间：
2019
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通讯作者：
S. Teitel
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作者：
Theodore A. Marschall;Daniel C Van Hoesen;S. Teitel
我们使用数值模拟来研究由固定有限应变率 $dotgamma$ 下均匀稳态简单剪切驱动的无热、无摩擦、软核二维球圆柱的双分散混合物的流动。能量耗散是通过相对于均匀剪切的主流体的粘性阻力来实现的，从而给出了具有牛顿流变学的非布朗悬浮液中的流动的简单模型。考虑到低 $dotgamma$ 下的一系列堆积分数 $phi$ 和粒子非球面性 $alpha$，我们研究了剪切流引起的粒子的角旋转 $dot heta_i$ 和方向排序 $mathbf{S}_2$，发现随着 $phi$ 变化的非单调行为。我们将这种非单调行为解释为从发生单粒子行为的低 $phi$ 区域到大 $phi$ 区域的交叉，在大 $phi$ 区域，减少的自由体积抑制运动并导致粒子旋转的随机泊松过程。我们表明，当接近干扰时，角度波动遵循临界比例。我们证明向列有序 $mathbf{S}_2$ 在稳态下具有恒定值，并且当受到扰动时，它通过单个粒子的不相干旋转松弛到稳态。我们证明，接近圆形粒子的极限 $alpha o 0$ 是奇异的，并且干扰及干扰以上的 $mathbf{S}_2$ 在此极限下保持有限。我们还考虑了纯剪切下粒子的行为，并与简单剪切下的粒子行为进行对比。我们讨论了粒子密度、向列排序和角速度的空间相关性，并表明这些相关性仍然是短期的。我们讨论尺寸单分散颗粒系统和形状多分散系统的各个方面。我们特别表明，对于嵌入圆盘海洋中的少量细长球柱，剪切会导致球柱的局部聚集。
We use numerical simulations to study the flow of a bidisperse mixture of athermal, frictionless, soft-core 2D spherocylinders driven by a uniform steady-state simple shear at a fixed finite strain rate $dotgamma$. Energy dissipation is via a viscous drag with respect to a uniformly sheared host fluid, giving a simple model for flow in a non-Brownian suspension with Newtonian rheology. Considering a range of packing fractions $phi$ and particle asphericities $alpha$ at low $dotgamma$, we study the angular rotation $dot heta_i$ and orientational ordering $mathbf{S}_2$ of the particles induced by the shear flow, finding a non-monotonic behavior as $phi$ is varied. We interpret this non-monotonic behavior as a crossover from a low $phi$ region where single particle-like behavior occurs, to a large $phi$ region where reduced free volume inhibits motion and leads to a random Poisson-like process for particle rotations. We show that angular fluctuations obey a critical scaling as jamming is approached. We show that the nematic ordering $mathbf{S}_2$ has a constant value in the steady-state, and that when perturbed it relaxes to the steady-state via an incoherent rotation of individual particles. We show that the limit $alpha o 0$, approaching circular particles, is singular and that $mathbf{S}_2$ at and above jamming stays finite in this limit. We also consider the behavior of particles under a pure shear and contrast with that under simple shear. We discuss spatial correlations for particle density, nematic ordering, and angular velocity, and show that these correlations remain short ranged. We discuss aspects of systems of particles monodisperse in size and systems polydisperse in shape. In particular we show, that for a dilute number of elongated spherocylinders embedded in a sea of circular disks, shearing results in a local clustering of the spherocylinders.