Numerical investigation of processes in strongly nonequilibrium Knudsen layers

Numerical solutions of model kinetic equations in Knudsen layers on surfaces with strong evaporation into the corresponding gas and excitation of internal degrees of freedom of the molecules are considered. It is shown that excitation of the molecules has a strong influence on the structure of the Knudsen layers and the parameters of the evaporating gas.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 72–81, May–June, 1981.     

Nonequilibrium kinetics of the gas-phase reactions of high-velocity molecules: Description by perturbation methods and simulation by statistical methods

Data on the numerical solution of a system of kinetic Boltzmann equations for a homogeneous multicomponent mixture of reacting gases with molecules of different “colors” that change in the reactions are given. The solution is obtained using a well-known version of the direct statistical simulation (Monte-Carlo) method, namely, the majorant frequency method, under conditions when the molecules belonging to the high-velocity “tails” of the corresponding distribution functions enter into the color change reaction. The properties of the numerical solution are compared with solutions obtained within the framework of the usual perturbation methods. It is shown that to obtain correct solutions over the range of threshold molecular velocities it is necessary to modify substantially the procedure of the perturbation method, while the traditional approach can be used only on the range of thermal particle velocities. Earlier, this was definitely established for distributions of the reacting molecules over their internal degrees of freedom and for the distributions of reactant-molecules participating in a high-threshold reaction. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 176–184, May–June, 2000. The work was carried out with financial support from the Russian Foundation for Fundamental Research (project No. 96-01-00573) and the Government Program for Leading Science Schools (grant No. 96-15-9603).     

Estimation of the effect of vibrational excitation of diatomic molecules on their diffusional transport and dissociation in a boundary layer

Relations for the diffusion fluxes of vibrationally highly excited diatomic molecules are found by means of the Chapman-Enskog method. On the basis of these relations a quantitative estimate of the changes in the diffusion coefficients under vibrational excitation and the corresponding changes in the macroscopic dissociation rate is obtained under conditions of disequilibrium of the upper vibrational levels of the dissociating molecules caused by the diffusion processes. The diffusion relations obtained are used in deriving the boundary conditions for the equations of level vibrational kinetics. A simplified version of this derivation is presented for noncatalytic and catalytic surfaces.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 169–182, January–February, 1996.     

Properties of the nonequilibrium high-velocity “Tails” of the molecular distribution function in plane couette flow of a compressible gas

The results of an analytic and numerical investigation of the properties of the high-velocity “tails” of the distribution function are given for the solution of the BGK model of the kinetic Boltzmann equation for plane Couette flow of a compressible gas. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 183–190, July–August, 1998. The work was carried out with financial support from the Russian Foundation for Basic Research (project No. 96-01-00573; grant in support of leading science schools No. 96-15-9603).     

Modification of the first approximation of the Chapman-Enskog method for a gas mixture

The authors propose a transformation of the equations of the first approximation of the Chapman-Enskog method for a gas mixture with frozen internal degrees of freedom. As a result, the solution for the perturbation of the distribution functions can be written in terms of the diffusion velocities and temperature gradient, and the derivation of the Stefan-Maxwell relations and the heat flux calculations can be much simplified. The transformations are extended to a mixture of polyatomic gases with nonequilibrium excitation of the internal degrees of freedom of the molecules. The modification of the first approximation of the Chapman-Enskog method does not affect the relations used for calculating the viscosity of the mixture. Accordingly, that part of the solution is not considered.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 178–185, July–August, 1992.     

Gas–Dynamic Structures in Supersonic Combustion of Hydrogen in a System of Plane Jets in a Supersonic Flow

Results of numerical and theoretical studies of supersonic diffusive combustion of a system of plane hydrogen jets in a supersonic air flow are described. It is shown that large–scale vortex structures appear in the mixing zone of the system of hydrogen jets and the cocurrent flow. These vortex structures affect the mechanism of turbulent exchange between the fuel and the oxidizer.