Self-Localization of the Energy Supply During Pulse Ionization of a Supersonic Flow

The pulse ionization of the time-dependent quasi-two-dimensional flow developed during diffraction of a shock wave on a wedge is investigated experimentally. The redistribution of the pulse volume discharge plasma subjected to preionization by ultraviolet radiation from plasma sheets is investigated when the discharge is initiated in different stages of the time-dependent gas dynamic flow. Images of the plasma flow are compared with the corresponding fields of the gas dynamic flow parameters. It is shown that the pulse discharge plasma flows can be controlled due to the phenomenon of self-localization in a given flow zone of known shape. The local energy supply to the gasdynamic flow is simulated numerically using the experimental data.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 144–156.Original Russian Text Copyright © 2005 by Znamenskaya, Ivanov, Kryukov, and Kuli-Zade.     

Numerical investigation of the growth of glowing discharges in two-dimensional geometry

It is known that a breakdown in gases can take place in two fundamental ways: by diffusion (the Townsend breakdown) or by forming a narrow current channel (the streamer breakdown). At present there are no reliable criteria for one or another of these mechanisms to occur. It is also an open question as far as the pressure region p < 10 mm Hg [I] is concerned. Even in the case of special preionization it is not always possible to avoid the streamer stage breakdown. It is obvious that the fundamental cause of a streamer breakdown is related to higher intensity of the electric field around the localized zone of higher conductivity [2]. In [3] the superiority was shown of using numerical methods in the analysis of an axisymmetric cathode directed streamer between two flat electrodes in nitrogen. In the present article the results are described of computations carried out to find out whether a mechanism is feasible for fusing the discharge at any early stage of ignition for the geometry of a flat electrode plane, which is the most favorable to an anode-oriented streamer. This effect was investigated within the framework of a nonstationary system of three equations in which the ionization processes, the recombinations in the balance of charged particles as well as the effect if space charge on the electric-field distribution have been taken into account [4], One has ignored the diffusion, which is also favorable to the streamer breakdown.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 49–54, September–October, 1978.The authors would like to express their thanks to A. A. Vedenov, A. P. Napartovich, and A. N. Starostin for their unceasing interest in this work and useful discussions.     

Growth of a nanosecond pulsed discharge in a gas with one-electron initiation

Pulse breakdown on gaps of millimeter order at substantial overvoltages is explained in terms of a discharge mechanism involving photoelectric emission from the cathode followed by collisional multiplication in the gas to give avalanches. The mechanism is used to deduce a theoretical equation for the time of discharge buildup in one-electron mutation, which is compared with experiment.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 40–45, January–February, 1971.     

Reduction of gas breakdown voltage with pulsed ionizing radiation

An algorithm is described for computer calculation of the dynamic breakdown voltage of a gas gap affected by a spatially uniform pulse of ionizing radiation. The algorithm is based on numerical integration of a system of nonlinear equations with integral boundary conditions. The program is used to calculate the breakdown voltage of an air gap affected by a bell-shaped ionizing pulse. It is shown that the relative reduction in breakdown voltage can amount to tens of percent for a radiation exposure dose rate P₀ 10⁸ R/sec.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 52–60, November–December, 1973.     

A contribution to the theory of streamer breakdown

The development of a systematic theory of streamer breakdown of a gas requires the consideration of the transport of the region of ionization toward the ionized gas in an electric field depending on the form of the streamer, which in turn is determined by the transport mechanisms [1–3]. In this form the problem is very complicated,and the theory takes the path of investigation of different qualitative models of a streamer [4]. It is assumed in [4] that the rates of anode-directed and cathode-directed streamers are determined by the drift velocity of the electrons. The mechanism of propagation of anode-directed streamers is taken to be the development of avalanche from the leading front of the electrons traveling to the anode. On the side of the cathode, electrons before the front of the cathodedirected streamer are produced due to the transport of radiation from the ionized region [1]. It is shown in [5] that direct photo-ionization is ineffective because of the small range of the quantas, and a mechanism of development of cathode-directed streamer related to the associative ionization of excited atoms is proposed. These atoms are formed by long-span resonance photons from the wings of the spectral line. An interesting prediction of the theory [4] was a linear dependence of the velocity of the streamers on their length. This dependence was confirmed in experiments on the study of streamer breakdown initiated at the center of the discharge gap in spark chambers [6, 7]. At the same time, for streamers developing from avalanche initiated at one of the electrodes the velocity of propagation of the breakdown wave remains constant with a good accuracy in gaps having lengths of the order of 1 m. In the present work a qualitative theory is developed which permits one to calculate the velocity of the an ode-directed streamer in the case where it is independent of the length. Since for pressures of the order of atmospheric pressure the diffusion coefficient of excited atoms [8] is comparable with the electron diffusion coefficient, the effect of radiation transport is disregarded. The stability of the front of the streamer to infinitely small perturbations is investigated. It is shown that, when the finite thickness of the front is taken into consideration, the streamer is stable. It is unstable in the approximation of infinitely thin leading fronts.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 56–65, January–February, 1973.The authors thank A. A. Vedenov, E. P. Velikhov, A. P. Napartovich, and O. B. Firsov for valuable discussions.     

Triggering regime of oil-filled trigatron dischargers

A comparative analysis made in [1, 2] of different types of regulable high-voltage dischargers with liquid insulation showed that trigatrons are currently the most promising for use in high-voltage pulse-operated devices due to their simplicity and reliability. Two basic mechanisms of discharge initiation can be realized in trigatrons — initiation by intensification of the field in the region of the control electrode [2, 3], and triggering by a spark in the ignition gap [4, 5]. The first type of trigatron has been studied sufficiently only for short voltage periods [3, 6, 7], so it is used mainly in switching the pulse-shaping lines of powerful nanosecond pulse generators with rapid (0.5–1.5 sec) charging [8, 9]. Almost no use is now made of the second type of trigatron switch in high-voltage pulse technology due to its unsatisfactory time characteristics. Here we report results of a study of the time characteristics of both types of oil-filled trigatrons operating in a regime whereby they form the leading edge of rectangular voltage pulses with amplitudes up to 800 kV and durations of 1–100 sec. The goal is to find the optimum conditions for triggering of trigatron dischargers with liquid insulation in the region of microsecond voltage discharges. Experiments were conducted on the unit in [10]. The test discharger was placed in a cylindrical chamber 45 cm in diameter and 27 cm in length. The high-voltage electrode of the discharger was in the form of a cylinder 20 cm in diameter positioned coaxially inside the chamber. The 10-mm-diameter ground electrode was positioned radially in a branch pipe 8 cm long. The control electrode was placed in a 2-cm-diameter hole in the center of the ground electrode. The chamber with the test discharge was filled with transformer oil with a breakdown voltage of about 50 kV. The oil was not replaced or cleaned during the experiment. We did not find that contamination of the oil by discharge products had any effect on the time characteristics of either type of discharger. The results were analyzed by the least squares method, with 50 measurements to a point (it was found that time lag of the discharger triggering conforms approximately to a normal distribution law for both types of discharger).Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 26–31, November–December, 1986.     

Some problems of centrally symmetrical percolation of a gas

A solution is considered for the centrally symmetrical problem of unsteady inflow of gas to a stratum sampler on a logging cable in a thick stratum with constant pressure at the discharge and variable pressure when filling the closed cylinder of the sampler with gas.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 117–121, November–December, 1971.     

Electrical breakdown in air in a transverse magnetic field

The electrical breakdown of gases in a transverse magnetic field is discussed in references [1–16]. Attention has mainly been concentrated on the case of coaxial electrode geometry [1–10]. The existing experimental data on breakdown between plane-parallel electrodes [11–14] relate to a narrow range of variation of the parameters characterizing breakdown (P, d, H, U). The author has made an experimental study of the process of electrical breakdown in air in a transverse magnetic field between plane-parallel electrodes of finite size in the pressure interval from 650 to 5·10^–3 mm Hg at gap lengths of from 1 to 140 mm and magnetic inductions from 0 to 10 600 G.     

Comparison with experimental data of computer simulations of the expansion of spark breakdown in air

Calculated results obtained earlier by means of a computer in the simulation of the expansion of spark breakdown in air are compared with the data of an experiment.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 182–184, July–August, 1979.I thank V. P. Korobeinikov for supplying the originals of the photographs of [2].     

Stratification of a gas by an incandescent wire

The propagation of a shock wave in a gas in which there is a wire rendered incandescent by a pulsed electrical discharge enables one to discover the stratified structure in space acquired by the gas as a result of nonuniform heating.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1984.     

Pressure wave breakdown of a gas film in a liquid-filled slit

In [1–4] the results of investigating the breakdown of gas bubbles by medium-intensity pressure waves are presented and various bubble breakdown mechanisms are proposed. It is shown that breakdown may occur as a result of the formation of a cumulative jet on the boundary of the bubble or as a result of instability due to the relative motion of the bubble in the wave. In [5] experimental data on the pressure wave breakdown of a gas film in a liquid on a solid wall are reported. It is shown that at wave amplitudes p/p₀1 a liquid jet is formed at the edge of the gas film. The jet, traveling along the wall, strips off the film and carries it into the surrounding liquid. Below we investigate the pressure wave behavior of a gas film in a liquid-filled slit.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.5, pp. 175–178, September–October, 1992.     

Blast wave propagation in air from a gaseous charge

In the point explosion problem it is assumed that an instantaneous release of finite energy causing shock wave propagation in the ambient gas occurs at a space point. The results of the solution of the problem of such blasts are contained in [1–4]. This point model is applied for the determination of shock wave parameters when the initial pressure in a sphere of finite radius exceeds the ambient air pressure by 2–3 orders of magnitude. The possibility of such a flow simulation at a certain distance from the charge is shown in papers [4, 5] as applied to the blast of a charge of condensed explosive and in [6, 8] as applied to the expansion of a finite volume of strongly compressed hot gas. In certain practical problems the initial pressure in a volume of finite dimensions exceeds atmospheric pressure by a factor 10–15 only. Such cases arise, for example, in the detonation of gaseous fuel-air mixtures. The present paper considers the problem of shock wave propagation in air, caused by explosion of gaseous charge of spherical or cylindrical shape. A numerical solution is obtained in a range of values of the specific energy of the charge characteristic for fuel-air detonation mixtures by means of the method of characteristics without secondary shock wave separation. The influence of the initial conditions of the gas charge explosion (specific energy, nature of initiation, and others) is investigated and compared with the point case with respect to the pressure difference across the shock wave and the positive overpressure pulse.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 110–118, May–June, 1986.     

Shock–Free Breakup of Droplets. Temporal Characteristics

In the present paper, we consider the shock–free breakup of droplets in their encounter with a layer (sheet) of a moving gas in the absence of pressure perturbations when the droplets are affected by a short U–shaped pulse of aerodynamic forces. Under a high pressure of the ambient gas medium p₀ = 20—80 bar, the droplets (ethanol or liquid oxygen) have a chance to break up after stay in a thing (2—5 mm thick) gas layer (jet) moving with a velocity of 1—10 m/sec. A distinctive feature of the process is that the characteristic time of droplet deformation and the period of natural oscillations coincide with the residence time for the droplets in the region of their interaction with the gas stream. Empirical formulas are proposed for determination of the total breakup time and the duration of the droplet disintegration stage in shock–free breakup.     

Nonequilibrium condensation of metal vapor mixed with an inert gas in nozzle expansion in cluster beam generators

A closed mathematical model of flows of a mixture consisting of a homogeneously condensible vapor and an inert gas is described. This model is a further development of the pure metal vapor condensation model [1 – 4] and, as distinct from the latter, makes it possible to take into account the effect of molecules of inert gas not only on the thermodynamics of the mixture but on the detailed kinetics of the processes of the cluster formation and breakdown. The results of numerical calculations of the formation of iron and silver clusters in experimental installations are presented.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 80–91, May–June, 1995.     

“Bunched” model of corona discharge in a gas-dynamical flow

In the present paper, a theoretical model of corona discharge is proposed for the case when electric charge transport is implemented by means of the motion of discrete charged bunches of finite dimensions. A system of equations and boundary conditions is formulated for the study of unsteady cyclic processes in a corona discharge. The electric field induced by the space charge of bunches and the presence of an external electric circuit are taken into account. A solution of the formulated system of equations for corona discharge with spherical geometry is obtained. The integrated (current-voltage) characteristics and the amplitude-frequency characteristics of the corona discharge are found. The proposed theory is generalized to the case of a corona discharge in a moving gas. The unsteady characteristics of corona discharge with spherical geometry for gas motion in a radial direction are found.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 153–160, January–February, 1986.The authors wish to express their gratitude to V. A. Likhter and V. I. Shul'gin for their useful discussions and valuable observations.     

Hypersonic flow past a wing at large angles of attack with detached shock wave

The thin shock layer method [1–3] has been used to solve the problem of hypersonic flow past the windward surface of a delta wing at large angles of attack, when the shock wave is detached from the leading edge (but attached to the apex of the wing) and the velocity of the gas in the shock layer is of the same order as the speed of sound. A classification of the regimes of flow past a delta wing at large angles of attack has been made. A general solution has been obtained for the problem of three-dimensional hypersonic flow past the wing allowing for nonequilibrium physicochemical processes of thermal radiation of the gas at high temperatures.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 149–157, May–June, 1985.     

Thermo-gravitational convection in a continuous optical discharge

The relative importance of such processes as the free convective motion of the gas, the absorption of the laser radiation and radiative heat transfer is discussed. The burning of a continuous optical discharge under experimental conditions [6] is theoretically investigated. The two-dimensional problem of the convective motion of the gas in an optical discharge burning in a vertical CO₂ laser beam inside a cylindrical chamber is solved. The principal characteristics of thermogravitational convection of the radiating air under conditions of local thermodynamic equilibrium at atmospheric pressure are studied on the temperature interval from 300 to 20 000°K.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 124–129, July–August, 1989.     

Selecting gas dynamics channel parameters for electrical discharge fast flowrate lasers

Using lasers with powers over l kW has become common in industry. Compactness and high efficiency are important requirements to take into account when designing lasers. Fast flowrate CO₂ lasers with independent discharges have wide application in industry, whose radiators are quite large because of the low density of the working gas. When considering the compactness and efficiency of these lasers, one must not ignore questions concerning the optimal correspondence of the characteristics for the pumping device (PD) of the gas and for the closed gas dynamics channel (CGDC) of the laser radiator. The PD must ensure circulation of the gas at a rate determined by the assigned power of the laser for the smallest size of the radiator and for small noise and vibration levels. The configuration and dimensions of the CGDC, the means of arranging its elements, the characteristics of the gas flow in the pumping zone, and the power of the active medium all determine the gas resistance of the closed channel and the loss of power at pump, which is 5 to 25% of the total power required in lasers with powers up to 10 kW [1, 2]. One may find information on the application of various PD in fast flowrate lasers [3–9], but there is no data on the characteristics of closed CGDC, which are determined by the PD parameters. There is currently an absence of literature dealing with the selection of optimal parameters for the electrical discharge, the gas flow, and the configuration of the flow section of the CGDC. We will take a comprehensive approach to determine the parameters for the gas flow in the pumping zone and the gas characteristics for the contour elements and the pumping device.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 3–8, November–December, 1986.     

Heat and mass transfer at the surface of glass-graphite materials in a high-temperature flow of gas

The article discusses the mutual effect of vaporization and combustion processes during the breakdown of glass-graphite materials in a hypersonic flow of gas. It demonstrates the possibility of the appearance of a nonunique dependence of the vaporization rate on the temperature of the heated surface. The effect of the composition of a material on the principal characteristics of the process of its breakdown is established.Moscow. Translated from Izvestiya Akademii Nauk SSSR. Mekhanika Zhidkosti i Gaza, No. 6, pp. 71–87, November–December, 1972.     

Flow in the neighborhood of the stagnation line on a blunt body traveling at supersonic speed through a zone with elevated temperature and vibrational energy of the molecules

The unsteady flow in the neighborhood of the stagnation line on a sphere traveling at supersonic speed through a plane layer of diatomic gas with elevated temperature and nonequilibrium excitation of the molecular vibrations is investigated. (The source of the inhomogeneity could be a gas discharge [1].) The problem is solved using the viscous shock layer model which makes it possible to take molecular transport processes into account and analyze the unsteady heat transfer. Such flows were previously calculated in [2] within the framework of the inviscid gas model.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i GazNo. 3, pp. 183–185, May–June, 1990.