Elaboration of collisional–radiative models for flows related to planetary entries into the Earth and Mars atmospheres

Abstract

The most relevant way to predict the excited state number density in a nonequilibrium plasma is to elaborate a collisionalradiative (CR) model taking into account most of the collisional and radiative elementary processes. Three examples of such an elaboration are given in this paper in the case of various plasma flows related to planetary atmospheric entries. The case of theoretical determination of nitrogen atom ionization or recombination global rate coefficients under electron impact is addressed first. The global rate coefficient can be implemented in multidimensional computational fluid dynamics calculations. The case of relaxation after a shock front crossing a gas of N 2 molecules treated in the framework of the Rankine-Hugoniot assumptions is also studied. The vibrational and electronic specific CR model elaborated in this case allows one to understand how the plasma reaches equilibrium and to estimate the role of the radiative losses. These radiative losses play a significant role at low pressure in the third case studied. This case concerns CO 2 plasma jets inductively generated in high enthalpy wind tunnels used as ground test facilities. We focus our attention on the behaviour of CO and C 2 electronic excited states, the radiative signature of which can be particularly significant in this type of plasma. These three cases illustrate the elaboration of CR models and their coupling with balance equations.

Status and Prospects on Nonequilibrium Modeling of High Velocity Plasma Flow in an Arcjet Thruster

“…While in the case of high velocity plasma flow, such as a high-velocity plasma flow in arcjet nozzle, the situation is more complicated: the characteristic time associated to the convective derivative D/Dt may decrease sufficiently to give a significant role even for highly excited species. Although the plasma flow is steady, the chemical reactions source term (qn(p)/qt) C,R , may be time dependent [56,57]. Therefore, the calculation of the temporal evolution of the population densities in high velocity plasma flow is needed.…”

Dissociative recombination in reactive flows related to planetary atmospheric entries

“…These elementary collisional processes take place simultaneously with elementary radiative processes, the list of which is given in [5,6]. The possible self-absorption of radiation by the flow is taken into account through the escape factor due to Holstein [22] for which a Doppler-type broadening has been assumed.…”

Vibrational and electronic collisional-radiative model in air for Earth entry problems

“…The general mass balance equation written for each species X j on its excited state i is then reduced to a simple form involving the volume of reference V(t) containing the number X j i of the concerned particles. 33 The number density is therefore ½X j i ¼ X j i =VðtÞ. Due to the total number of species and states considered in CoRaM-AIR, the set of balance equations can be written as the following system of 995 non linear coupled ordinary differential equations:…”