Molecular simulation of flows in thermochemical non-equilibrium around a cylinder using ab initio potential energy surfaces for N2 + N and N2 + N2 interactions

Abstract

We present two-dimensional direct molecular simulation (DMS) results for high-enthalpy nitrogen flows in thermochemical non-equilibrium around a circular cylinder. The simulations are carried out using accurate ab initio potential energy surfaces (PES) to describe N2 + N and N2 + N2 interactions. Select comparisons with the direct simulation Monte Carlo method are presented to demonstrate how the high-fidelity DMS data, both at the level of bulk flow quantities and local molecular distributions, can be used to thoroughly inform or validate simplified reduced-order descriptions. Then, a partially dissociated nitrogen flow around a circular cylinder is obtained from two successive refinements of a well-established ab initio nitrogen PES. The only input in both calculations is the respective PESs, all other simulation parameters being precisely equal. This work, enabled by large scale computing, represents the first attempt at establishing a rigorous methodology for (i) the validation of lower-fidelity, computationally efficient models using ab initio, assumption-free calculations (DMS) as benchmarks and (ii) a systematic assessment of ab initio PES accuracy using entire flow field results.