Domenico Bruno

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.

Thermodynamics and transport properties of thermal plasmas: the role of electronic excitation

The role of electronic excited states in affecting the thermodynamic and transport properties of thermal plasma is investigated in the temperature range [300‐100 000 K] and in the pressure range [1‐10 3 atm] for hydrogen and [10 −2 ‐10 3 atm] for nitrogen. Thermodynamic functions have been calculated modelling in different ways the electronic levels of atomic species (ground-state, Debye‐H¨ uckel and confined-atom approximations). Frozen and reactive specific heats as well as isentropic coefficients are strongly affected by the electronic excitation whereas compensation effects smooth its influence on the total specific heat, i.e. the sum of frozen and reactive contributions. Higher-order approximations of the Chapman‐Enskog method have been used to evaluate transport coefficients, including electronically excited states as separate species. The importance of a state-to-state approach to calculate transport coefficients is presented taking into account the strong dependence of transport cross sections on the principal quantum number. Results for hydrogen, nitrogen and air plasmas are widely discussed.

Gas-surface scattering models for particle fluid dynamics: a comparison between analytical approximate models and molecular dynamics calculations

Abstract A parametric study is performed to test the validity of some of the most common models of gas-surface scattering used in particle simulations of rarefied flows. The simplified models are compared with results of semiclassical molecular dynamics trajectory calculations for inelastic scattering of Xe atoms on GaSe. The simple models are shown to be inadequate to accommodate all the features of the real dynamics. Sample calculations of oxygen heterogeneous recombination on silica are also provided to emphasise the importance of vibrationally state-resolved models.

Collision integrals for interactions involving atoms in electronically excited states.

Transport collision integrals for low-lying excited states of nitrogen atoms and ions are derived in the framework of a phenomenological approach following, where possible, also the traditional multipotential procedure. The two sets of results are compared considering critically the observed deviations, and finally, the proposed model is validated by comparison with oxygen atom-atom interactions. In addition, an attempt is made to extend the proposed phenomenological method to interactions involving high-lying excited states, taking into account the symmetric interaction of two excited hydrogen atoms, characterized by increasing principal quantum number.

Calculation of Transport Coefficients with Vibrational Nonequilibrium

An extended Enskog asymptotic expansion method is used to find approximate solutions of the Boltzmann equation in the cases of strong thermal nonequilibrium. The formalism to determine thermal conductivities in the expanding flow of a binary mixture of a diatomic and its parent atoms through a supersonic nozzle is applied

Transport properties of high-temperature air in a magnetic field

Transport properties of equilibrium air plasmas in a magnetic field are calculated with the Chapman–Enskog method. The range considered for the temperature is [50–50u2009000] K and for the magnetic induction is [0–300] T.

Extracting Cross Sections from Rate Coefficients: Application to Molecular Gas Dissociation

E = collision energy, J e = unit vector F = least mean-square measure of distance between two rate coefficients, cm s 2 k T = rate coefficient, cm s 1 KB = Boltzmann constant, JK 1 mr = reduced mass, kg NT = number of temperature points considered in minimization process P = vector of independent variables parametrizing a given functional form for a cross section T = temperature, K = cross section, A

Fully Coupled Maxwell/Navier-Stokes Simulation of Electromagnetic Hypersonics Including Accurate Transport Models

A Navier-Stokes solver for non-equilibrium aerothermodynamics is coupled with a fully implicit solver of the Maxwell equations. Transport phenomena are modelled using a high accurate Chapman-Enskog method that accounts for the effects of concentration, pressure and temperature gradients and provides anisotropic diffusion velocity, heat flux and viscosity in the presence of a magnetic field. Gas neutrality is not enforced so that the electric charge density can be locally different from zero. Numerical tests are carried out on a flatfaced cylinder to test the capabilities of the implicit Maxwell solver and of the coupled Maxwell/Navier-Stokes system.

Particle kinetic modelling of rarefied gases and plasmas

We show that Monte Carlo methods can be usefully applied to particle transport problems in the challenging conditions set up by the merging of two fields: rarefied gas dynamics and cold plasmas. The simulation of these systems, in fact, requires us to analyse the foundation of the method in order to develop transport modelling techniques that can take into account at the same time the non-equilibrium kinetics of the scattering medium. We demonstrate this point by providing examples extracted from the work of our group in the fields of cold plasmas, rarefied gas dynamics and coherent kinetics.