The calculation of drag on nano-cylinders

Abstract

The study of molecular flows at low Knudsen numbers (∼0.1–0.5), over nano-scaled objects of 20–100 nm size is becoming an important area of research. The simulation of fluid–structure interaction at nano-scale is important for understanding the adsorption and drag resistance characteristics of nano-devices in the fields of drug delivery, surface cleaning and protein movement. A novel formulation has been proposed that calculates localised values for both the kinetic and configurational parts of the Irving–Kirkwood stress tensor at given fixed positions within the computational domain. Macroscopic properties, such as streaming velocity, pressure and drag coefficients, are predicted by modelling the fluid–structure interaction using a moving least-squares method. The gravitation-driven molecular flow is examined over three different cross-sectional shapes—i.e. diamond-, circular- and square-shaped cylinders—confined within parallel walls and has been simulated for rough and smooth surfaces. The molecular dynamics formulation has allowed, for the first time, the calculation of localised drag forces over nano-cylinders. The computational simulation has shown that existing methods, including continuum-based approaches, significantly underestimate drag coefficients over nano-cylinders. The proposed molecular dynamics formulation has been verified on simulation based tests, as experimental and analytical results are unavailable at this scale. Copyright © 2016 John Wiley & Sons, Ltd.