Fundamental Processes in High-Temperature Hypersonic Flows
EMSL Project ID
49215
Abstract
Hypersonic aerodynamics involves the reactions of atmospheric molecules at up to 20,000 K. Hypersonic vehicles, spacecrafts and re-entry vehicles are in the atmosphere for extended periods of time; thus their surface is exposed to high-temperature interactions to gases. Instead of characterizing a hypersonic flight environment and then selecting an appropriate thermal protection system (TPS) that can survive the environment, it would be a significant technological step forward if the TPS could be engineered to alter the hypersonic flight environment itself (i.e. the boundary layer). The development of materials that have favorable interactions with the boundary layer environment requires a fundamental understanding of gas-surface interactions as well as the chemical and physical processes that take place at molecular level. The currently applied chemical models in hypersonic flow simulations are partially based on outdated data and assumptions. Chemical models used in hypersonic computational fluid dynamics (CFD) codes rely on limited experimental data. Accurate four-body potential energy surfaces for gas-phase bimolecular collisions of atmospheric molecules are needed for realistic computational fluid dynamics (CFD) simulations of shock layers around hypersonic vehicles. Therefore, we are developing theoretical and computational methods to understand the dynamics of molecule-molecule and atom-molecule collisions and the catalytic surface atomic oxygen recombination of the key atmospheric molecules. This enables more realistic hypersonic flow simulations of shock layers around the vehicles. We are developing global ground-state potential energy surfaces (PESs) for the collision of atmospheric molecules like N2 and O2, that are suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation. The surfaces are based on electronic structure calculations by multi-state complete-active-space second-order perturbation theory with minimally augmented correlation-consistent polarized valence triple-zeta basis sets. Electronic structure calculations are performed, followed by fitting potential energy surfaces and their couplings. The global ground-state potential energy surfaces are obtained by fitting the many-body interaction to electronic structure data points with a fitting function that is a permutationally invariant polynomial in terms of bond-order functions of the six interatomic distances. The global PESs include subsurfaces describing the interaction of diatomic molecules with diatomic molecules or with atoms as well as interactions of triatomic molecules with an atom. The resulting surfaces are used to carry out dynamical simulation that allows one to get reaction rate constants and energy transfer rate constants to model heat transport. As the work continues it is being expanded to include electronically excited states and electronically nonadiabatic couplings.
Project Details
Start Date
2016-02-19
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members