I. Armenise

Nonequilibrium vibrational kinetics in the boundary layer of re-entering bodies

Nonequilibrium vibrational distributions of N2 in the boundary layer surrounding a blunt body in hypersonic flow have been calculated by coupling the nonequilibrium vibrational kinetics, the dissociation and recombination processes, and the boundary-layer equations. The role of different energy exchange processes [vibration-vibration (V-V), vibration-translation (V-T), and recombination-dissociation] in affecting vibrational kinetics has been studied by considering each process. Then the complete kinetics are taken into account, obtaining a global view of the interplay of the different microscopic processes. The model used for the recombination/dissociation processes is such to selectively pump levels v = 25 and 45 of the N2 vibrational manifold. This vibrational energy is then redistributed by V-V and V-T processes. As a result, strongly nonequilibrium vibrational distributions are obtained, despite the thermalizing action of the V-T processes by nitrogen atoms.

State-to-state approach in the kinetics of air components under re-entry conditions

AIAA, Fluid Dynamics Conference, 27th, New Orleans, LA, June 17-20, 1996 A state to state vibrational kinetics for air components including recombination-dissociation processes as well as the formation of NO through the reaction between vibrationally excited nitrogen molecules and atomic oxygen has been inserted in a monodimensional fluid dynamic code, describing the boundary layer surrounding a body under reentry conditions. The results show that the formation of NO is strongly enhanced by the nonequilibrium vibrational distribution of N2 formed during the recombination process. This kind of distribution is responsible of a non-Arrhenius behavior of dissociation constants of N2 and O2 as well of the NO formation rate as a function of instantaneous temperature. (Author)

Reduction of State-to-State Kinetics to Macroscopic Models in Hypersonic Flows

The state-to-state chemical kinetic model, which considers a kinetic equation for each vibrational state of diatomic molecules, has been applied to some supersonic flow regimes and in particular in boundary layer, nozzle expansion, and shock wave. Nonequilibrium vibrational distribution obtained in the calculations shows strong departure from equilibrium-inducing non-Arrhenius global chemical rates, which differ substantially from macroscopic rates commonly used in fluid-dynamic codes. The evolution properties of the distribution have been investigated by a zero-dimensional numerical code in controlled conditions. We are trying to obtain from zero-dimensional results the approach to find appropriate macroscopic rate models to be used in fluid-dynamic codes accounting for the vibrational nonequilibrium. A comparison of analytical fitting of the zero-dimensional data and fluid dynamic global rates has been performed. Nomenclature ci = coefficients for the solution of the master equation Ev = energy of the vth vibrational level k = Boltzmann constant k d = dissociation rate constant k p = rates of the process p

Non-equilibrium plasma kinetics: a state-to-state approach

State-to-state approaches are used to shed light on (a) thermodynamic and transport properties of LTE plasmas, (b) atomic and molecular plasmas for aerospace applications and (c) RF sustained parallel plate reactors. The efforts made by the group of Bari in the kinetics and dynamics of electrons and molecular species are discussed from the point of view of either the master equation approach or the molecular dynamics of elementary processes. Recent experimental results are finally rationalized with a state-to-state kinetics based on the coupling of vibrational kinetics with the Boltzmann equation for the electron energy distribution function.

Nitrogen Nonequilibrium Vibrational Distributions and Non-Arrhenius Dissociation Constants in Hypersonic Boundary Layers

A ladder-climbing model including V ‐ V (vibration‐ vibration) and V ‐ T (vibration‐ translation ) energy exchange processes linked to state-to-state dissociation ‐ recombination kinetics has been developed and inserted in the e uid dynamics equations, describing the boundary layer surrounding a noncatalytic surface hit by a hypersonic e ow of atomic and vibrationally excited molecular nitrogen. The results show a strong overpopulation of vibrational levels with respect to Boltzmann distributions along the coordinate perpendicular to the surface and the corresponding non-Arrhenius behavior of dissociation constants.

Thermodynamics, Transport and Kinetics of Equilibrium and Non-Equilibrium Plasmas: A State-to-State Approach

Thermal non-equilibrium plasmas have been deeply investigated theoretically by means of the state-to-state approach, offering the unique opportunity of a detailed information about internal distributions affecting thermodynamics, transport coefficients and kinetics, properly accounting for the presence of excited states. The efforts made in the construction of knowledge on the dynamics of elementary processes occurring in the plasma with resolution on internal degrees of freedom, required by the method, are discussed. Boltzmann equation is solved for electrons self-consistently coupled to the chemical species collisional dynamics, reproducing very interesting features of strongly non-equilibrium internal distributions, characterizing plasmas.

State-to-State Catalytic Models, Kinetics, and Transport in Hypersonic Boundary Layers

A new iterative model has been developed that couples, in the boundary layer of a reentering body, the equations for N 2, N, O 2, O, and NO mass fractions, N 2 and O 2 vibrational distributions, and gas temperature with the surface state-to-state heterogeneous recombination coefficients has been developed. Results for SiO 2 and metallic surfaces are presented and discussed. The non-Boltzmann behavior of the vibrational distribution functions near the surface is found, as well as the nonmonotonic behavior of the NO density profile along the boundary layer coordinate. The transport coefficients and the heat flux to the surface are calculated using the Chapman-Enskog theory. A strong dependence of transport coefficients and energy flux on the vibrational-chemical kinetics in the boundary layer is shown. In particular, the diffusion coefficients of the first and last vibrational levels differ by several orders of magnitude, according to the shape of vibrational distributions, and the surface material noticeably influences diffusion coefficients of N and NO.

Nonequilibrium Kinetics and Heat Transfer in O2/O Mixtures near Catalytic Surfaces

Nonequilibrium vibrational-chemical kinetics and heat transfer in an O 2/O mixture near the surface of a space vehicle under reentry conditions are studied. Vibration-translation, vibration-vibration energy exchange, dissociation-recombination processes in the gas phase as well as heterogeneous recombination, dissociation, and deactivation of vibrational states on a silica surface are taken into account. The effect of nonequilibrium kinetics and surface catalysis on the total heat e ux and averaged dissociation-rate coefe cients is examined. It is shown that both heterogeneous recombination and dissociation on the surface must be incorporated in the kinetic scheme. The contribution of thermal conductivity, thermal and mass diffusion, and vibrational energy diffusion to theheat transfer is evaluated. In particular, vibrational energy diffusion near the surface is found to play an important role.

Influence of Nonequilibrium Kinetics on Heat Transfer and Diffusion near Re-Entering Body

The heat transfer and diffusion near the surface of a space vehicle under re-entry conditions are studied on the basis of the kinetic theory of gases. The influence of the nonequilibrium kinetics in an (N 2 , N) mixture on the transport properties of the flow is investigated. The nonequilibrium vibrational distributions in the boundary layer near the surface of the re-entering body have been obtained in the state-to-state approach and Inserted in the transport kinetic theory code. As a result, the total heat flux, thermal conductivity, and all diffusion coefficients are calculated under different conditions in the freestream and on the surface. The effects of various energy exchanges, vibrational nonequilibrium, dissociation, and recombination on the heat transfer and diffusion are examined

Nonequilibrium Vibrational Kinetics of an O/O Mixture Hitting a Catalytic Surface

The importance of a silica surface in affecting both the state-to-state kinetics and the macroscopic properties of an O2/O mixture hitting a blunt body at hypersonic speed has been investigated. First, the surface has been considered catalytic only for recombination: three different assumptions are examined and compared with the resultsfrom a noncatalytic surface model. Second, both deactivation and dissociation aretreated in theframework of a catalytic surface. Nomenclature Ca = q a/q CM = q M/q Cv = q v/q Cwa = q wa/q w D(M/a)m = diffusion coefe cient of the species M/a in the mixture,m 2 s i 1