Multiscale Simulations for Polymeric Flow

TL;DR

This paper introduces multiscale simulation methods combining microscopic and macroscopic models to accurately capture the flow behavior of simple and polymeric fluids across different dimensions and complexities.

Contribution

It develops a unified multiscale framework that directly computes local stresses from microscopic simulations, incorporating memory effects for polymeric flows in multiple dimensions.

Findings

Successfully applied to simple fluids, capturing local stress without flow history.

Extended to polymeric liquids, incorporating memory effects via MD simulations.

Implemented a Lagrangian CFD approach for 2D/3D polymer flow with slow relaxation.

Abstract

Multiscale simulation methods have been developed based on the local stress sampling strategy and applied to three flow problems with different difficulty levels: (a) general flow problems of simple fluids, (b) parallel (one-dimensional) flow problems of polymeric liquids, and (c) general (two- or three-dimensional) flow problems of polymeric liquids. In our multiscale methods, the local stress of each fluid element is calculated directly by performing microscopic or mesoscopic simulations according to the local flow quantities instead of using any constitutive relations. For simple fluids (a), such as the Lenard-Jones liquid, a multiscale method combining MD and CFD simulations is developed based on the local equilibrium assumption without memories of the flow history. (b), the multiscale method is extended to take into account the memory effects that arise in hydrodynamic stress due to the slow relaxation of polymer-chain conformations. The memory of polymer dynamics on each fluid element is thus resolved by performing MD simulations in which cells are fixed at the mesh nodes of the CFD simulations.For general (two- or three-dimensional) flow problems of polymeric liquids (c), it is necessary to trace the history of microscopic information such as polymer-chain conformation, which carries the memories of past flow history, along the streamline of each fluid element. A Lagrangian-based CFD is thus implemented to correctly advect the polymer-chain conformation consistently with the flow. On each fluid element, coarse-grained polymer simulations are carried out to consider the dynamics of entangled polymer chains that show extremely slow relaxation compared to microscopic time scales.