A NEW OUTER BOUNDARY-CONDITION FOR MOLECULAR-DYNAMICS SIMULATIONS AND ITS APPLICATION TO A RAREFIED-GAS FLOW PAST A CYLINDER (PERIODIC-SHELL BOUNDARY-CONDITION)

The present paper proposes a new outer boundary condition called the 'periodic-shell boundary condition' which is used for molecular dynamics simulations on a flow around a body. This boundary condition is devised to diminish the influences of limitedness of simulation regions by making molecules inside regions interact with outside imaginary molecules which are replicas of actual molecules existing near boundary surfaces. In using this condition we need no information about temperature, density and averaged velocity at boundaries, which is in contrast with the case of ordinary uniform flow conditions where such information is indispensable. To clarify the availability of the present boundary condition we have carried out the simulations of a rarefied gas flow past a circular cylinder. The results of simulations show that the periodic-shell boundary condition significantly diminishes the distortions of flow fields compared with the conventional conditions, such as uniform flow and free-outflow conditions. Such improvements enable us to use smaller simulation regions and lead to a dramatic derease in computation times.