Analysis of Chemistry-Vibration Coupling in Diatomics for High Enthalpy Nozzle Flows

A state-specic model is developed to analyze the complex chemistry-vibration coupling present in high enthalpy nozzle o ws. A basic model is formulated assuming molecules are formed at a specic vibrational level and allowed to relax through a series of vibrationvibration and vibration-translation processes. This is carried out assuming that the molecules behave as either harmonic or anharmonic oscillators. The results are compared with the standard vibration-chemistry model for high enthalpy nozzle o ws. Next, a prior recombination model that accounts for the rotational - vibrational coupling is used to obtain prior recombination distribution. A distribution of recombining states is obtained as a function of the total energy available to the system. The results of this model are compared with recent experiments. I. Introduction In high enthalpy nozzle o ws, the expanding o w is often dominated by recombination reactions. Typically these recombining species form molecules that have substantial internal energy. One of the assumptions in non-equilibrium o ws is that the atoms recombine to form molecules at the local vibrational temperature. The vibration-vibration relaxation takes place at a much faster rate than other processes enabling the o w to be characterized by single vibrational temperature. The present work relaxes that assumption by analyzing the o w using a state-specic model. The state-specic model which deals with molecules in each vibrational state as a separate chemical species precludes the need to use a model for vibrational relaxation. The vibration-vibration and vibration-translation processes are treated as chemical reactions. The state-specic approach has been used before to analyze o ws in hypersonic nozzles 1, 2 and shock tunnels. 3 In this work, we focus on a simple diatomic molecule and consider its vibrational and dissociation/recombination behavior. In the rst part of this work, we force the recombining species to form a molecule at a pre-dened vibrational energy level. The molecule thereby has substantial internal energy, and then it relaxes through a series of vibration-vibration and vibration-translation processes. Both harmonic and anharmonic oscillator assumptions are used to describe the relaxation processes. The results are compared with a standard