Yu. V. Tunik

Investigation of oxygen dissociation and vibrational relaxation at temperatures 4000–10 800 K

The oxygen absorbance was studied at wavelengths 200-270 nm in Schumann-Runge system behind the front of a strong shock wave. Using these data, the vibrational temperature Tv behind the front of shock waves was measured at temperatures 4000-10,800 K in undiluted oxygen. Determination of Tv was based on the measurements of time histories of absorbance for two wavelengths behind the shock front and on the results of detail calculations of oxygen absorption spectrum. Solving the system of standard quasi-one-dimensional gas dynamics equations and using the measured vibrational temperature, the time evolution of oxygen concentration and other gas parameters in each experiment were calculated. Based on these data, the oxygen dissociation rate constants were obtained for thermal equilibrium and thermal non-equilibrium conditions. Furthermore, the oxygen vibrational relaxation time was also determined at high temperatures. Using the experimental data, various theoretical and empirical models of high-temperature dissociation were tested, including the empirical model proposed in the present work.

Dispersion of the detonation products of a condensed explosive with solid inclusions

The dispersion of detonation products of a condensed explosive charge is numerically investigated; the charge is spherical and contains chemically inert solid particles uniformly distributed throughout its volume. The calculations are based on a two-speed, two-temperature model of interpenetrating continua, one of which consists of the gaseous detonation products or the atmosphere, while the other is the medium corresponding to the chemically neutral heavy particles.

Numerical modeling of detonation combustion of hydrogen-air mixtures in a convergent-divergent nozzle

The flow of igniting hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered. A possibility of stabilizing detonation combustion is numerically investigated at different freestream Mach numbers with account for nonuniform distribution of hydrogen concentration at the nozzle entry. The investigation is performed on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical reactions is used. The calculated thrust is compared with the drag of a conical housing containing the supersonic nozzle considered.

Stabilization of detonation combustion in a high-velocity flow of a hydrogen-oxygen mixture

The flow of a hydrogen-oxygen mixture diluted with argon in a supersonic axisymmetric nozzle consisting of an inlet cylinder, a convergent region, a cylindrical throat, and a divergent region is considered. The supersonic flow enters the channel along the axis of symmetry. The flow structure is calculated with allowance for hydrogen ignition. A possibility of stabilizing the combustion zone is studied and the forces acting on the nozzle from the flow are determined. The problem is solved in the two-dimensional approximation with account for detailed combustion kinetics.

Propagation of turbulent burning of methane-air mixtures in tubes

A simplified mathematical model for turbulent flows, which may be called a “two-phase” approximation with respect to one of possible methods of deriving corresponding equations for time-averaged quantities, is proposed. In a one-dimensional approximation, the problem of propagation of a turbulent flame that arises near the butt end of a semi-infinite smooth tube is solved. On the basis of the infinitely thin flame front model, the range of concentrations in which turbulent burning modes with a constant flame-propagation velocity exist is determined.

Equilibrium and non-equilibrium rate constants of oxygen dissociation at high temperatures

Basing on the measurement of oxygen vibrational temperature behind the front of a strong shock wave, the parameters of high-temperature gas flow were calculated. The oxygen dissociation rate constants were obtained for thermal equilibrium conditions as well as for thermal non-equilibrium ones. The expression for the thermal equilibrium dissociation rate constant was obtained at temperatures near the front 6000-11000K. The simulation of high-temperature oxygen flow behind the front of the shock wave was performed in quasi-one-dimensional approximation. The empirical model of high-temperature dissociation is proposed for the description of the temperature evolution behind the front of shock wave, and the calculated profiles of vibrational and translational temperatures were compared with the measured ones.

Stability of detonation combustion with respect to the variation in the hydrogen concentration at the supersonic nozzle inlet

Detonation combustion of hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered. The nozzle geometry does not ensure gas self-ignition; for this reason, forced ignition is used, which, under certain conditions, leads to the formation of stationary detonation combustion in the case of both uniform and nonuniform hydrogen distribution at the channel entry. The nonlinear problem of the stability of these combustion regimes against periodic disturbances of the hydrogen concentration in the oncoming flow is numerically solved. The study is performed on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical reactions is used.

Shock Tube Investigation of Molecular Oxygen Dissociation at Temperatures of 4000 to 10800 K

The quantitative experimental data on the vibrational temperature of dissociating molecules are informative characteristic for the evaluation of the relationship between the rates of vibrational relaxation and dissociation and for the development of suitable theoretical models of these processes. The evident lack of such data has already resulted in a explosive increase in the number of various dissociation models [1]. The technique of the measurement of the vibrational temperature of oxygen molecules behind the wave front under thermal and chemical nonequilibrium conditions was described earlier [2]. In the present work the evolution of the vibrational temperature T v behind the strong shock front was used for determination of oxygen dissociation rate constants and vibrational relaxation time under the thermal nonequilibrium conditions. This allows the testing of some of the theoretical models of thermal nonequilibrium dissociation.

Initiation of detonation combustion for coal dust in a methane-air mixture

This paper studies the combustion of coal dust behind the leading shock wave in a mixture of oxygen with acetylene and in air with different contents of methane. The model of combustion processes for coal dust is presented. The possibility of initiation of heterogeneous detonation in air with a low methane content is considered. It is shown that the distance at which heterogeneous detonation forms decreases by 3% with a mass concentration of coal dust of 0.14 g/m/sup 3/. The effect of radiation weakens the process of carbon sublimation, thus limiting the increase in particle temperature.

Instability of Contact Surface in Cylindrical Explosive Waves

In this paper are developed modifications of the Godunov scheme, based on Kolgans scheme of the second order of accuracy in the spatial variables for smooth solutions. It is constructed schemes of the first and the variable order of approximation, which exceed the Godunov scheme in accuracy. Referencing to the system of differential equations for propagation of flat sound waves in a gas at rest, the Kolgan scheme and the first-order schemes obtained are investigated onto the ability to ensure the non decrease of entropy, that is, to product of physically justified numerical solutions. The test problems of nonlinear gas dynamics on the decay of a discontinuity in a pipe and the transformation of a non uniformity in a plane-parallel flow are solved. Cylindrical explosion task is considered as the main one. The stability of a contact discontinuity behind a blast wave is investigated numerically in the Cartesian and polar coordinate systems. Analysis of obtained and published solutions does not confirm the instability of the contact discontinuity which initially has the circular shape. Change of the shape of initially perturbed break is largely caused by the instability of Taylor, not Richtmyer-Meshkov. Calculations are partially fulfilled using supercomputer “Lomonosov” of Moscow state university.