Liquid flow past nanoscale objects

We present nonequilibrium molecular dynamics (MD) simulations of liquid flow past a carbon nanotube (CNT) and a single graphene sheet. We apply a gravity driven liquid argon flow past a CNT in a small domain and show that the drag coefficients can be modeled as Stokes flow past an array of CNT's with an effective diameter. The effective diameter can be obtained from the radial density profile around the CNT. We also apply a uniform flow of liquid argon and SPC/E water past a graphene sheet and show that the drag coefficient and the velocity profile can be modeled using Navier-Stokes equation provided corrections are applied to the equation. The corrections are the effective shape of the graphene sheet, the slip velocity correction and the viscosity and density layering correction. The effective shape can be obtained from the density profile plot around graphene. We use a separable solution of the elliptical cylindrical Stokes equation as a physical model to determine the slip velocity at the boundary of the effective shape by extrapolation. The viscosity and density layering correction is determined by calculating the local average density around the graphene sheet and using a viscosity equation of state. By applying these corrections, we show that good agreement between computational fluid dynamics (CFD) and MD can be obtained. Using a very large domain, agreement is also obtained between an analytical expression of the drag coefficient on an ellipse in an unbounded uniform flow derived by matched asymptotic expansion and MD for the case of strong interaction between argon and carbon atoms. Agreement is obtained for high Reynolds number for the weak interaction case as well