Upscaling ab-initio chemistry models to non-equilibrium flow simulations.

摘要

Thermo-chemical nonequilibrium is generated by hypersonic vehicles, high-speed combustion, detonations, and other devices that rapidly heat the gas, as in shock waves, and convect it before a new equilibrium state is reached. Nonequilibrium affects reaction rates, heat transfer, aero-loads, flame stability and other critical engineering processes. Due to the difficult of measuring high enthalpy nonequilibrium processes, modern reaction and internal energy exchange models are phenomenological. They are able to reproduce available equilibrium data but they are inaccurate under nonequilibrium conditions. The work in this thesis replaces the phenomenological models by upscaling ab-initio calculations. There are two main challenges in linking ab-initio calculations to full flowfield simulations. First, the needed ab-initio surfaces for many collision partners are not available. Second, the produced state-to-state cross section datasets are too large to be efficiently implemented in engineering simulations. These challenges are addressed by building engineering-accuracy potentials and proposing new efficient reaction and energy exchange models, based on maximum entropy considerations. The new models reduce both the number of required quasi-classical calculations and the collision parameter databases. Although the work in this thesis focuses on O2+O interactions because of prevalence of oxygen in flight, all developed models may be applied to other diatom-atom interactions and can be extended to other diatom-diatom combinations.