Nonequilibrium Gas Flows Research Articles

Conservation laws and growth of discontinuities in a reactive polytropic gas

We shall consider a conservation law associated with a non-equilibrium gas flow with chemical reaction. Some results on the growth of discontinuities and the occurrence of breakdown of the solution are pointed out.

Laser diagnostics of molecular states in nonequilibrium gas flows

Laser diagnostics techniques are developed, and some typical results are presented on the vibrational CO2 molecule level population measurements under highly nonequilibrium conditions for two types of flows: (i) in a conventional gasdynamic lasers and (ii) in a flow mixing gasdynamic laser. The measuring procedure is based on recording spectral gain coefficient distributions at several resolved rotational transitions of different vibrational bands. The laser optical system with spatial selection of single lines is described. The system allows fast (about 10−5−10−4 s) line tuning, thus providing a variable and arbitrary choice of the selected line sequences. The optimum choice of the laser generation spectrum is discussed, and the sources of measuring uncertainties are analyzed. Typical illustrations and results are given and discussed.

Numerical Solution of the Nonlinear Boltzmann Equation for Nonequilibrium Gas Flow Problems

The field of fluid mechanics is rapidly advancing, driven by unprecedented volumes of data from experiments, field measurements, and large-scale simulations at multiple spatiotemporal scales. Machine learning (ML) offers a wealth of techniques to extract ...Read More

Numerical Solution of the Nonlinear Boltzmann Equation for Nonequilibrium Gas Flow Problems

The field of fluid mechanics is rapidly advancing, driven by unprecedented volumes of data from experiments, field measurements, and large-scale simulations at multiple spatiotemporal scales. Machine learning (ML) offers a wealth of techniques to extract ...Read More

Plasma generation in vibrationally nonequilibrium molecular gas flows

2014 Experimental and theoretical studies are made of the associative molecular gas ionization phenomena in N2 and CO under the adiabatic expansion and cooling of a shock-heated gas. It is shown that for a wide range of conditions, the contribution of the associative ionization mechanism substantially exceeds (by several orders of magnitude) the thermal one. Revue Phys. Appl. 17 (1982) 15-20 JANVIER 1982, PAGE

Investigation of isothermal flow of a mixture of gas and particles in a channel of variable section

Isothermal flow of a gas with particles is investigated analytically, which makes it possible to analyze all possible flow regimes in channels of different shapes. It is shown that in a channel of constant section there are two possibilities: either an equilibrium regime is established with constant flow parameters, or the gas reaches the velocity of sound, and then further flow in the channel is impossible (“blocking” of the channel). In a contracting nozzle, “blocking” also occurs if the channel is sufficiently long. In an expanding nozzle when there are particles in the gas with a velocity lower than the gas velocity, it is possible to have flow regimes with transition through the velocity of sound: a subsonic flow goes over into a supersonic flow and, conversely, it is also possible to have a flow in which there is “blocking” of the channel, which is quite different from the flow of a pure gas in an expanding nozzle and is due to the influence of interphase friction on the flow. The variation of the pressure along the flow can be nonmonotonic with points of local maximum or minimum which do not coincide with the singular point at which the gas velocity reaches the velocity of sound. In the case of nonequilibrium gas flows with particles in a Laval nozzle, the velocity of the gas may become equal to the isothermal velocity of sound not only in the exit section of the nozzle or in its expanding part, as noted in [4–6], but also at the minimal section, since it is possible to have flows for which the velocities of the phases are equalized at this section.

The onset of converging and diverging shock waves in non-equilibrium gas flows

In this work, the effects of thermodynamical influences and that of wave front curvature on the propagation of finite amplitude waves of arbitrary shape and their consequent formation into shock waves are examined.

Method of measuring vibrational temperatures in thermodynamically nonequilibrium gas flows

A numerical calculation is made of the integral radiation of CO2 molecules in the 2.7- and 4.3-μm bands and of CO molecules in the 4.7-μm band when the vibrational temperatures significantly exceed the rotational and translational temperatures.

An algorithm for calculating two-dimensional non-equilibrium gas flows

An algorithm for calculating two-dimensional non-equilibrium gas flows

Application of the asymptotic method to the analysis of chemically nonequilibrium gas flows

Application of the asymptotic method to the analysis of chemically nonequilibrium gas flows

Application of the splitting method for calculating two-temperature and ionizationally non-equilibrium gas flows

The possibility is considered of using the splitting method for the numerical solution of non-stationary gas-dynamic problems, taking into account the physical processes most widespread in a high-temperature gas—ionization of atoms and equalization of the electronic and atomic (ionic) temperatures. The results of numerical calculations carried out by the proposed algorithm are presented.

Researches in the gasdynamics of explosion and reacting systems

The papers presented at the colloquium and the results from personal discussions indicate that the numerous applications of combustion and explosion processes in rocketry, industrial technology, and in safe handling of fuels during transportation have meant that researches on the gasdynamics of explosive phenomena are being vigorously pursued in the USA, France, Britain, Japan, and other industrially developed countries. Particular interest attaches to evidence presented at the colloquium on methods of calculating shock-wave parameters for large-scale explosions of gases and fuels, together with definition of the critical conditions for detonation propagation in chemically active media, as well as analysis of turbulent mixing and combustion in gases and heterogeneous systems. In particular, turbulent mixing, combustion, and detonation have major applications in laser engineering, and it has been shown, for instance, that separate excitation and turbulent mixing of nonequilibrium high-temperature gas flows can substantially improve the efficiency and optical characteristics of high-power gasdynamic laser systems. Efficient optical methods of diagnosis for combustion, detonation, and explosion processes have been developed in the USA and France, and these deserve attention and further study for use in experimental research. This applies particularly to laser Raman spectroscopy and laser holography.

Method of computing the chemically nonequilibrium gas flow in a heated tube in almost equilibrium or frozen states

The solution of equations describing turbulent isobaric flow of a chemically reacting gas in a heated tube is investigated analytically. Solutions of the ordinary nonlinear differential equations are obtained for almost frozen flow by the perturbation method, and for almost equilibrium flow by an asymptotic method taking account of the zero and first approximations, Linear differential equations in variations are written down to find the subsequent approximations.

Derivation of a linear theory for nonequilibrium and equilibrium flows

Conventional linear theory of nonequilibrium and equilibrium gas flows yields correct results only for very small deviations of the stream parameters from the unperturbed values. Moreover, if in linearization we take the coordinates in planar flow as independent variables, then the flow past concave and convex corners is described in exactly the same fashion. In this case the characteristic emanating from the corner is (depending on the type of corner) a compression or rarefaction shock. In the case of a break in the wall of an axisymmetric channel the shock intensity approaches infinity with approach to the centerline, which indicates a deficiency of this type of linear theory. In the following we use a modification which eliminates the deficiencies noted above. This involves conversion to new independent and dependent variables such that the coefficients of the exact equations being linearized become weakly varying functions of the unknown parameters, the linearized boundary conditions coincide with the exact conditions at all or part of the boundaries, and the rarefaction shocks become rarefaction wave bundles of finite width. The last condition is achieved as a result of the fact that, in accordance with the Lighthill method of deformable coordinates [1], we take as one of the independent variables a quantity which maintains a constant value on each characteristic of the bundle of characteristics emanating from the break point [for equilibrium flows the semicharacteristic (or characteristic) independent variables were used in deriving the linear theory, for example, in [2–4]]. The study was based on the example of two-dimensional stationary nonequilibrium flow of an inviscid and nonheatconducting gas. In this case we find that boththelinear equations at a finite distance from the walls and the boundary conditions for determining the potential and nonequilibrium parameters outside the rarefaction wave bundles coincide with the equations and the conditions of conventional linear theory [5], while the relations associating the values of the parameters on the closing characteristics of each bundle (outside the bundles the same value of the characteristic variable corresponds to these characteristics) at some distance from the axis or from some reflecting surface are identical to the conditions on the rarefaction shocks. This fact makes it possible to use several results of conventional linear theory.

Conservation Equations for the Non-Equilibrium Radiative Flow

A set of conservation equations for the non-equilibrium radiative gas flow has been derived on the basis of the multi-component kinetic theory of gases to the order of the Navier-Stokes approximation. The gross effects of non-equilibrium radiation and ionization have been incorporated in the resultant equation by the use of appropriate rate equations with respect to certain related processes. The final form of the set of conservation equations thus provides the basis to examine various effects of non-equilibrium radiative gas flow to different orders of approximations of the continuum description of the radiative gasdynamic problem.

Study of the nature of hypersonic nonequilibrium gas flow past blunt bodies

Study of the nature of hypersonic nonequilibrium gas flow past blunt bodies

Computer experiments related to chemical propulsion.

I. Introduction T HE use of high-speed computers has played an increasingly important role in the analysis of problems relating to chemical propulsion. In many cases the is merely used for the straightforward evaluation of the analytical expressions resulting from theoretical analysis; however, in an increasing number of problems the has played a central and indispensable role, being used as an apparatus to test theoretical models of the phenomenon under study. The use of such computer experiments'7 to study problems related to chemical propulsion forms the subject of the present survey. It is proposed that a experiment be defined as a theoretical analysis in which the use of the plays the central role in evaluating the consequences of the mathematical model of the physical phenomenon or process being studied. All such experiments involve first a formulation of the problem, second the development of a numerical scheme for solving the equations describing the process in question, then the actual computations, which would generally be impossible without modern high-speed computers, and finally an evaluation and interpretation of the results. The boundary between what can be classed as a experiment and a straightforward calculation will be somewhat arbitrary. Computer experiments take several different forms. In certain cases the physics of the problem is completely understood; however, the mathematical equations describing the phenomenon in question are intractable to analytical solution without the use of severe assumptions. Then high-speed computers are used to numerically evaluate the consequences of the equations. The calculations, made by Fromm 1 and others, of viscous flows over obstacles, and resulting in movies of the computed flow solutions, provide an outstanding example of this type of experiment. In other problems the detailed physics or the value of key physical constants may be uncertain. Thus, for example, reaction rate constant values needed to compute nonequilibrium gas flows may be known only to an accuracy of several orders of magnitude. Such problems are sometimes approached by developing a mathematical model that includes all possible factors of importance. Computer experiments or extensive calculations are then made to establish which factors are important, and which can be ignored. Duff's2 calculations of detonation structure which were carried out for several possible values of the key reaction rate constant provide an early example of this type of experiment.

On the equations of nonequilibrium gas flows

On the equations of nonequilibrium gas flows