Multi Scale Mechanics, Faculty of Engineering Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
J Chem Phys. 2012 Jul 28;137(4):044711. doi: 10.1063/1.4737927.
We present molecular dynamics simulations of planar Poiseuille flow of a Lennard-Jones fluid at various temperatures and body forces. Local thermostatting is used close to the walls to reach steady-state up to a limit body force. Macroscopic fields are obtained from microscopic data by time- and space-averaging and smoothing the data with a self-consistent coarse-graining method based on kernel interpolation. Two phenomena make the system interesting: (i) strongly confined fluids show layering, i.e., strong oscillations in density near the walls, and (ii) the stress deviates from the Newtonian fluid assumption, not only in the layered regime, but also much further away from the walls. Various scalar, vectorial, and tensorial fields are analyzed and related to each other in order to understand better the effects of both the inhomogeneous density and the anisotropy on the flow behavior and rheology. The eigenvalues and eigendirections of the stress tensor are used to quantify the anisotropy in stress and form the basis of a newly proposed objective, inherently anisotropic constitutive model that allows for non-collinear stress and strain gradient by construction.
我们展示了在不同温度和体积力下 Lennard-Jones 流体平面泊肃叶流动的分子动力学模拟。在靠近壁面的地方使用局部恒温器来达到稳态，直到达到极限体积力。宏观场是通过时间和空间平均从微观数据中获得的，并通过基于核插值的自洽粗粒化方法对数据进行平滑处理。两种现象使系统变得有趣：（i）强烈受限的流体表现出分层，即在壁附近密度出现强烈的振荡，以及（ii）应力偏离牛顿流体假设，不仅在分层区域，而且在远离壁面的区域也是如此。分析了各种标量、向量和张量场，并将它们相互关联，以便更好地理解不均匀密度和各向异性对流动行为和流变学的影响。应力张量的特征值和特征方向用于量化应力的各向异性，并为新提出的客观、固有各向异性本构模型奠定基础，该模型通过构造允许非共线的应力和应变梯度。
