Nitrogen Dissociation in Hypersonic Flows: A Molecular Dynamics Investigation

Jason Bender, University of Minnesota

A spacecraft entering Earth's atmosphere typically travels at many times the speed of sound, inducing a flow field characterized by strong shock waves, extreme temperatures and reactions between chemical species in the air. Computation plays a crucial role in analyzing these flows since experimental analysis is expensive or impossible. My research has focused on developing improved models of high-temperature chemical processes in hypersonic flows. Presently, such models are outdated and inadequate for simulations of advanced aerospace vehicles of interest to the Air Force, NASA, the Department of Energy and other organizations.

I will describe a molecular dynamics study of a key chemical reaction in hypersonic aerodynamics: dissociation of molecular nitrogen. Early work focused on the construction of accurate potential energy surfaces describing high-energy N2+N2 interactions based on a new electronic structure data set from the group of Donald G. Truhlar and on novel methods for fitting six-dimensional permutationally invariant surfaces. Then, dissociative collisions were simulated using the quasiclassical trajectory method, which considers all rovibrational quantum states of the collision partners with minimal simplifications. I will elaborate on key trends in the data from over 2.4 billion calculated trajectories, focusing on what the data reveal about how energy moves between the translational, rotational and vibrational modes of the dissociating gas. The research lays the foundation for macroscopic thermochemical models that are rigorously tied to first principles and I will discuss current efforts to incorporate the project's findings into computational fluid dynamics simulations.

Abstract Author(s): Jason D. Bender, Paolo Valentini, Ioannis Nompelis, Thomas Schwartzentruber, Graham V. Candler