Towards the Development of New Fundamental Thermochemical Models for Hypersonic Computational Fluid Dynamics

Jason Bender, University of Minnesota

Computational fluid dynamics (CFD) plays a crucial role in the development of future aerospace vehicles like new planetary re-entry systems and scramjet-powered aircraft. Presently, hypersonic reacting flows are simulated with empirical chemical models of inadequate quality for advanced applications, in which post-shock temperatures can reach as high as 20,000 K. We are pursuing a fundamental study of the physical chemistry of high-temperature aerospace flows with strong thermal nonequilibrium. Central to this effort is a collaboration between experts in compressible gas dynamics and computational chemistry. Using accurate multireference electronic structure methods and building on recent advances in nonadiabatic molecular dynamics, we are analyzing gas-phase reactions key to the fluid mechanics of extremely high-speed air. Our ultimate goal is to reduce these results into new macroscopic chemical models for US3D, an unstructured finite-volume CFD code developed at Minnesota for hypersonic reacting flows. Recent work has focused on the O4, N4, and O2N2 supermolecules. Electronic energies have been calculated using the CASSCF and CASPT2 ab initio methods for a range of geometric configurations encompassing the bond dissociation regimes. Six-dimensional potential energy surfaces have been constructed using the Local Interpolating Moving Least Squares (L-IMLS) method of D.L. Thompson, A.F. Wagner, M. Minkoff, et al. Early testing confirms that this fitting technique is both computationally efficient and highly accurate. Current efforts include classical and semiclassical trajectory calculations using the Adiabatic and Nonadiabatic Trajectories (ANT) code, also developed at Minnesota, to determine cross sections and reaction rates.

Abstract Author(s): Jason D. Bender, Graham V. Candler, Donald G. Truhlar, Sriram Doraiswamy, Ke Yang, Zoltan Varga, and Yuliya Paukku