Julien Annaloro

Global rate coefficients for ionization and recombination of carbon, nitrogen, oxygen, and argon

The flow field modeling of planetary entry plasmas, laser-induced plasmas, inductively coupled plasmas, arcjets, etc., requires to use Navier-Stokes codes. The kinetic mechanisms implemented in these codes involve global (effective) rate coefficients. These rate coefficients result from the excited states coupling during a quasi-steady state. In order to obtain these global rate coefficients over a wide electron temperature (Te) range for ionization and recombination of carbon, nitrogen, oxygen, and argon, the behavior of their excited states is investigated using a zero-dimensional (time-dependent) code. The population number densities of these electronic states are considered as independent species. Their relaxation is studied within the range 3000  K≤Te≤20 000  K and leads to the determination of the ionization (ki) and recombination (kr) global rate coefficients. Comparisons with existing data are performed. Finally, the ratio ki/kr is compared with the Saha equilibrium constant. This ratio increases more rapidly than the equilibrium constant for Te>15 000  K.The flow field modeling of planetary entry plasmas, laser-induced plasmas, inductively coupled plasmas, arcjets, etc., requires to use Navier-Stokes codes. The kinetic mechanisms implemented in these codes involve global (effective) rate coefficients. These rate coefficients result from the excited states coupling during a quasi-steady state. In order to obtain these global rate coefficients over a wide electron temperature (Te) range for ionization and recombination of carbon, nitrogen, oxygen, and argon, the behavior of their excited states is investigated using a zero-dimensional (time-dependent) code. The population number densities of these electronic states are considered as independent species. Their relaxation is studied within the range 3000  K≤Te≤20 000  K and leads to the determination of the ionization (ki) and recombination (kr) global rate coefficients. Comparisons with existing data are performed. Finally, the ratio ki/kr is compared with the Saha equilibrium constant. This ratio increases ...

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

The most relevant way to predict the excited state number density in a nonequilibrium plasma is to elaborate a collisional–radiative (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 N2 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 CO2 plasma jets inductively generated in high enthalpy wind tunnels used as ground test facilities. We focus our attention on the behaviour of CO and C2 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.

Collisional-Radiative Modeling Behind Shock Waves in Nitrogen

Nonequilibrium plasma, produced by the propagation of a shock wave in a shock tube or behind a shock front detached from a body entering a planetary atmosphere, requires the development of state-to-state models. The collisional-radiative model for N2 has been elaborated on in this framework for pure nitrogen flows. Its elaboration is reported in this paper. The model includes N2, N2+, N, N+, and free electrons in thermochemical nonequilibrium. The model is vibrationally and electronically specific insofar as the vibrational states of the electronic ground state of N2 and the electronic excited states of N2; and the electronic ground and excited states of N2+, N, and N+ are individually treated. These states are involved in collisional and radiative elementary processes, forming a set of around 40,000 basic data. This model is implemented in a one-dimensional flow, numerical code based on an Eulerian approach. Two test cases are treated at Mach numbers of around 30 and 40, the conditions of which relate to...

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

The two-temperature collisional-radiative model CoRaM-AIR, working over a wide range for pressure and temperatures, has been developed for the flow conditions around a space vehicle entering the Earths atmosphere. The species N2, O2, NO, N, O, Ar, N2+, O2+, NO+, N+, O+, Ar+, and free electrons are taken into account. The model is vibrationally specific on the ground electronic state of N2, O2, and NO, and electronically specific for all species, with a total of 169 vibrational states and 829 electronic states, respectively. A wide set of elementary processes is considered under electron and heavy particle impact given the temperatures involved (up to 30 000 K). This set corresponds to almost 700 000 forward and backward elementary processes. The relaxation from initial thermal or chemical nonequilibrium is studied for dissociation-ionization situations in conditions related to the FIRE II flight experiment. Boltzmann plots clearly prove that the vibrational and electronic excitation distributions are far...

Physico-Chemistry of Planetary Atmospheric Entry Plasmas

This contribution deals with the description of the physico-chemistry in the reactive flow produced near the surface of a body entering a planetary atmosphere in hypersonic regime. A shock layer is formed in which a boundary layer is developed where energy is released to the body surface. N2 is chosen as a test-case of Earth atmospheric reentry to illustrate the main characteristics of the flow. The vibrational and electronic specific Collisional-Radiative model CoRaM-N2 is described and implemented in a one-dimensional Euler flow solver. The well-known FIRE II flight experiment conditions are used to illustrate the behaviour of the different ground and excited states of atomic and molecular species. The results show that the three successive phases occur: vibrational excitation, dissociation and ionisation. Radiation plays a minor role. According to the upstream thermodynamic conditions, the boundary layer edge can be in local thermodynamic equilibrium or not. The different strategies using thermal protection systems are discussed to reduce the damaging of the entering body.

Computations of a Shock Layer Flow Field with Global and Detailed Chemistry Models

The present work is a first step in computing a reactive gas flow behind a shock wave with detailed collision-radiative models. If simulating high-temperature, high-enthalpy, non-equilibrium gas flows in shock layers has been widely done so far with global models for the chemical kinetics and the vibrational non-equilibrium, it is quite new to compute such flow fields with detailed chemistry models. This is now possible as the computation and memory resources of the computers allow to run CFD codes with detailed models. State-specific vibrational models are efficient to model both the chemical reactions and the vibrational non-equilibrium at once, without making strong assumptions (like Boltzmann distribution) as it the case with multi-temperature models for vibrational non-equilibrium modeling.

State-to-state modeling of non equilibrium low-temperature atomic plasmas

The most relevant approach leading to a thorough understanding of the behavior of non equilibrium atomic plasmas is to elaborate state-to-state models in which the mass conservation equation is applied directly to atoms or ions on their excited states. The present communication reports the elaboration of such models and the results obtained. Two situations close to each other are considered. First, the plasmas produced behind shock fronts obtained in ground test facilities (shock tubes) or during planetary atmospheric entries of spacecrafts are discussed. We focused our attention on the nitrogen case for which a complete implementation of the CoRaM-N2 collisional-radiative model has been performed in a steady one-dimensional computation code based on the Rankine-Hugoniot assumptions. Second, the plasmas produced by the interaction between an ultra short laser pulse and a tungsten sample are discussed in the framework of the elaboration of the Laser-Induced Breakdown Spectroscopy (LIBS) technique. In the p...

Elaboration of collisional-radiative models applied to Earth and Mars entry problems

Three Collisional-Radiative (CR) models are elaborated and tested in typical atmospheric entry conditions. The first CR model (CoRaM-AIR) is dedicated to the Earth atmospheric entry and is based on an electronically and vibrationally specific state-to-state description of N2-O2-Ar mixtures. The second CR model (CoRaM-MARS) is dedicated to the Mars atmospheric entry and treats the CO2-N2-Ar mixtures with a similar vibrationally and electronically specific approach. Since their implementation in a Computational Fluid Dynamics (CFD) code has not yet been performed, they are implemented in a 0D code giving the evolution in time of the excited states number density in constant pressure and temperature conditions similar to trajectory points at lower altitude. Nevertheless, such an implementation in a CFD code has been performed for a third CR model, specifically devoted to pure nitrogen flows (CoRaM-N2). The results show that the equilibrium is reached relatively slowly. In addition, the influence of radiation on the chemistry is weak.

Predictions of excited states population densities using the CoRaM-CO 2 code and confrontations with measurements obtained with the VKI-Plasmatron high enthalpy wind tunnel

ow conditions, the analysis of the non equilibrium is performed. We put forward the important role of the radiation. These results are then confronted with experimental ones obtained in the VKI Plasmatron high enthalpy wind tunnel: the inuence of electrons and the limitations of our approach are discussed.