Objective molecular dynamics of dissociating nitrogen under high temperature conditions

Abstract

We present a novel method of Objective Molecular Dynamics (OMD) for the study of air chemistry at high temperatures far-from-equilibrium flows commonly encountered in hypersonic conditions. The method gives a way of simulating a three parameter family of homogeneous incompressible, and a nine parameter family of general compressible, unsteady flows without incurring boundary effects, which is ideal for extracting bulk properties of the system. Besides the usual advantage of molecular dynamics simulations of relying only on a potential energy surface, OMD has an additional advantage. Here, only a finite number of atoms are simulated, and motions of all the other atoms (typically infinitely many) are given by applying an isometry group to the simulated atoms. All atoms, simulated and nonsimulated, satisfy exactly the equations of molecular dynamics for their forces. In this work, we use OMD to simulate an inviscid flow of homoenergetic compression of dissociating nitrogen gas and report the non-Boltzmann effects of overpopulation and underpopulation of the vibrational energy distribution. We also compare evolution of gas in an adiabatic reactor simulated by usingOMD to those simulated by a different modeling approach of Direct Molecular Simulation (DMS) for non-equilibrium initial conditions.