Application of ab-initio based grouped rates for modeling non-equilibrium flow physics

摘要

This work focuses on the use of ab-initio grouped rates obtained from the CG-QCT method and analytical expressions to model non-equilibrium chemical processes in hypersonic flows. The groups are made by dividing the energy spectrum of the molecule into equal energy intervals. The reduced order framework is derived from the multi-group maximum entropy model using a linear reconstruction function. This paper focuses on three different system of molecules which are of interest during reentry into Earth's atmosphere: (ⅰ) N_2(~1Σ_g~+)-N(~4S_u) collisions, (ⅱ) N_2(~1Σ_g~+)-N(~4S_u) and N_2(~1Σ_g~+)-N_2(~1Σ_g~+) collisions and (ⅲ) O_2(~3Σ_u~-)-O(~3P). The grouped rates for the nitrogen systems are obtained using the CG-QCT method considering the full set of ro-vibrational levels of nitrogen molecule whereas analytical expressions are used to compute the grouped rates for the oxygen system. The reduced order model is used in conjunction with CFD codes to predict the non-equilibrium behavior of high speed flows in one and two dimensions. Two different testcases are considered: (ⅰ) one-dimensional nozzle flow and (ⅲ) two-dimensional axi-symmetric flow over a sphere. The results are compared to the state-to-state simulation for the oxygen case since we have the state-to-state rates available for vibrational specific processes. We achieve good agreement with the state-to-state results for the non-equilibrium distributions. The strong state of non-equilibrium observed in the results lays emphasis on the need for computationally efficient models to simulated these high-enthalpy flows.