Microscale hydrodynamics: Discrete-particle simulation of evolving flow patterns

The technique of molecular-dynamics simulationin which the equations of motion of a system of interacting particles are solved numerically to yield the temporal evolution of the systemis used in a study of the flow of a two-dimensional fluid past a circular obstacle. The flow is observed to develop with time, passing through a series of well-defined patterns that bear a striking similarity with flow patterns observed experimentally in liquid and gas flow; the patterns include stationary eddies, periodic shedding of vortices, and a vortex street characterized by a Strouhal number close to the experimental value. Very large systemsby current molecular-dynamics standardsneed to be used in order to accommodate the obstacle and the region occupied by the structured wake, and the present work includes the largest such simulations carried out to date. Though more extensive work is called for, the results suggest that continuum hydrodynamics is applicable down to much shorter length scales than hitherto believed, and that the molecular-dynamics approach can thus be used to study certain kinds of hydrodynamic instabilities.