Comparison of DSMC Chemistry Models for Rarefied Shock Tube Simulations with Nitrogen

Abstract

Shocks encountered in high Mach number flows lead to dissociation of gas molecules. At present, the DSMC codes that simulate such flows under rarefied conditions account for dissociations using phenomenological models such as the total collision energy (TCE) model. However, these models calculate the cross sections using equilibrium rate constants and are not appropriate to use during non-equilibrium situations. The present work calculates cross sections using ab initio methods that first calculate a highly accurate potential energy surface (PES), followed by using the quasi-classical trajectory (QCT) method to generate cross sections. A shock tube under rarefied conditions containing nitrogen gas is simulated wherein cross sections are implemented using the ab initio method as well as the classical TCE model for comparison. The comparison shows a difference in the prediction of nitrogen dissociation for high enthalpy areas where non-equilibrium is expected.