Reduced kinetic mechanism for CFD applications

A reduced kinetic mechanism for the modeling of the behavior of the electronic states of the atomic species in air mixture is presented. The model is built by lumping the electronically excited states of the atomic species and by performing Boltzmann averages of the rate constants describing the elementary kinetic processes between electrons and the grouped states. To this aim, the detailed reaction rate constants compiled by A. Bultel and A. Bourdon in Ref. [1] are used. The rotational energy mode is assumed to quickly equilibrate with the translational energy mode at the kinetic temperature of the heavy species as opposed to the electronic and the vibrational structure of the molecular species, which is assumed to be in Boltzmann equilibrium at a common temperature T_V. The limited number of pseudo-states considered leads to a significant reduction of the computational cost, while preserving the accuracy of the more sophisticated collisional radiative models, and allows the application of these models to bi-dimensional and three dimensional flow solvers. The hybrid collisional radiative model, is used to analyze the strong non-equilibrium flow surrounding the FIRE II flight experiment during the early part of its re-entry trajectory. It is found that the reduced kinetic mechanism is capable of reproducing the ionizational non-equilibrium phenomena which is responsible for the strong decrease in the radiative heat loads on the space capsule during the re-entry phase.