Molecular dynamics simulation of flow around a circular nano-cylinder

TL;DR

This study uses molecular dynamics simulations to analyze wake flow around a nano-cylinder, revealing size effects, cavitation influence, and introducing the Jz number to understand internal fluid size effects.

Contribution

The paper introduces the Jz number to account for internal size effects and investigates the impact of cavitation and Brownian forces on wake flow at the nanoscale.

Findings

Reynolds number influences cavitation and wake flow characteristics.

The Jz number correlates with vortex shedding suppression.

Cavitation and Brownian forces significantly affect flow fluctuations.

Abstract

In this study, the wake flow around a circular nano-cylinder is numerically investigated with molecular dynamics simulation to reveal the micro/nano size effect on the wake flow. The cavitation occurring when Reynolds number (Re) > 101 can effectively influence the wake flow. The Strouhal number (St) of the wake flow increases with the Re at low Re, but steadily decreases with the Re after the cavitation appears. The dominant frequency of the lift force fluctuation can be higher than that of the velocity fluctuation, and be drowned in the chaotic fluctuating background of the Brownian forces when Re {\geq} 127. Also because of the strong influence of the Brownian forces, no dominant frequency of the drag force fluctuation can be observed. The Jz number, which is defined as the ratio between the mean free path {\lambda} of the fluid molecules and the equilibrium distance of potential energy {\sigma}, is newly introduced in order to consider the internal size effect of fluid. The St of the wake flow increases with the Jz until it falls to zero sharply when Jz {\approx} 1.7. It denotes the discontinuity of the fluid can eventually eliminate the vortex generation and shedding. Meanwhile, the St decreases with the Kn because of the intensification of the cavitation.