A Molecular Dynamics Simulation of the Turbulent Couette Minimal Flow Unit

TL;DR

This paper presents a molecular dynamics simulation of turbulent Couette flow, comparing it with CFD results, and explores molecular-scale effects on turbulence structures and statistics.

Contribution

It introduces a molecular-scale law of the wall and analyzes the impact of grid resolution on turbulence structures in MD simulations.

Findings

Qualitative similarity between MD and CFD turbulence structures

Excellent quantitative agreement in turbulence statistics

Dependence of spectral content on grid resolution

Abstract

A molecular dynamics (MD) simulation of planar Couette flow is presented for the minimal channel in which turbulence structures can be sustained. Evolution over a single breakdown and regeneration cycle is compared to computational fluid dynamics (CFD) simulations. Qualitative similar structures are observed and turbulent statistics show excellent quantitative agreement. The molecular scale law of the wall is presented in which stick-slip molecular wall-fluid interactions replace the no-slip conditions. The impact of grid resolution is explored and the observed structures are seen to be dependant on averaging time and length scales. The kinetic energy spectra show a range of scales are present in the molecular system and that spectral content is dependent on the grid resolution employed. The subgrid velocity of the molecules is compared to spatial averaged velocity using joint probability density functions. Molecular trajectories, diffusions and Lagrangian statistics are presented. The importance of sub-grid scales, relevance of the Kolmogorov lengthscale and implications of molecular turbulence are discussed.