Magnetogasdynamic Channel Research Articles

Structure of the Current Layer and Modes of Magneto-Gasdynamic Interaction with Supersonic Gas Flow

Numerical simulation of the interaction of the current layer in the magneto-gasdynamic channel with the induction of external magnetic fields of 1, 2, and 4 T and various load resistance values has been carried out. Features of the energy balance and differences in the temperature profiles in the current layers, which were both streamlined by a nonconducting gas flow and completely covered the channel cross section and interacted with the flow like a piston, are revealed. The dependences on the load resistance are obtained for the current, coefficients of current-layer permeability, and enthalpy conversion.

Computational Modeling of the Structure of a High-Current Discharge in a Magnetogasdynamic Channel

A two-dimensional computational model is proposed to calculate radiative-convective heat transfer in gas flows with large gradients of physical properties. The model is based on the numerical solution of the unsteady dynamic equations for a compressible inviscid gas and the radiative transfer equations. Flow calculations for the magnetogasdynamic channel of a rail accelerator show that the dynamics of the process is substantially affected by the flow in the discharge region and hydrodynamic instability, resulting in the nonstationarity and nonuniformity of the flow and discharge structure. During the process, the discharge can exist both in the form of several current-carrying channels and in the form of a unified plasma formation. Results of the numerical calculations agree qualitative with experimental data.

Local plasma parameters and integral characteristics of a magnetogasdynamic channel under conditions of ionization instability

Results are presented from an experimental investigation of the onset of ionization instability in a disk-shaped Faraday magnetogasdynamic channel attached to a shock tube. The experiments were carried out in a pure inert gas (xenon) without alkaline additives. A relation is found between the integral plasma characteristics of a nonequilibrium magnetogasdynamic channel and the local parameters of a plasma that is unstable against the ionization instability. Mechanisms for amplifying perturbations and increasing the effective conductivity are revealed. It is concluded that these effects stem mainly from the features of three-body recombination in rare gases.

Electron energy balance in an ionization-unstable plasma in a magnetogasdynamic channel

An experimental investigation was made of the evolution of ionization instability in a model of a disk-shaped Faraday magnetogasdynamic channel connected to a shock tube in a pure rare gas (xenon) with an alkaline additive. The main components of the average electron energy balance were determined: the Joule heating power, the average rate of energy transport of the heavy component by elastic collisions, and the average rate of energy lost through ionization. It was found that the electron energy defect which includes losses not taken into account, increases abruptly at supercritical values of the magnetic induction and accounts for approximately half of the Joule heating power. It is concluded that some of the electron energy is transferred to pulsations.

Determination of fluctuations of the electron temperature and density in an ionizationunstable inert-gas plasma in a magnetogasdynamic channel

Electron temperature and density fluctuations arising as a result of the development of ionization instability in nonequilibrium magnetogasdynamic channels, where a pure inert gas without alkali-metal seeding is used as the working gas, are studied in greater detail. An experiment was performed in a disk-shaped Hall-type magnetogasdynamic channel combined with a shock tube, with magnetic inductions greater than the inductance B c=0.57 T at which ionization inhomogeneities first appear in the experiment. The electron temperature and density were measured from the drop in the intensity of the continuous radiation in the UV region according to the Unsold-Kramers and Biberman-Norman theories. On the average, the electron temperature in inhomogeneities varies from 7000 to 10000 K and reaches its highest values in small-scale fluctuations. As a result of the absence of ionization equilibrium in the inhomogeneities, relatively small fluctuations of n e and a phase shift between the fluctuations of n e and T e are observed. At the same time, the average values of the electron density increase with the degree of supercriticality of the magnetic field. This evidently results in a higher effective conductivity.

Effect of an inhomogeneous magnetic field on the structure of an ionized gas flow

Results of an experimental study of the flow of an ionized gas produced by a shock wave through an inhomogeneous magnetic field are presented. Braking of the gas flow produced by the end currents is determined at two fixed sections of the magnetogasdynamic channel from the value of the isolated shock wave formed in the vicinity of the hemispherical model over which the flow passes. Maximum recorded reduction in Mach number was 30%, and with a magnetogasdynamic interaction parameter greater than 1.5, a transition of supersonic flow to infrasonic at the exit of the magnetic zone was observed. Experimental results were compared with a solution of a model problem which assumed one-dimensional flow in the flow core. The gas used was argon, with a maximum magnetic field induction of 1.5 T.

Effect of electrical conductivity of flow on current distribution in a magnetogasdynamic channel with allowance for the Hall effect

The effect of a magnetic field on the current distribution on a plane continuous anode situated opposite the cathode in a rectangular magnetogasdynamic channel with an external magnetic field was experimentally investigated. The distributions of the charged-particle density and the electron temperature near the outlet end of the electrodes were measured. The distribution of electrical conductivity in the flow was calculated. The electron density distribution along the channel is attributed to ambipolar diffusion of plasma to the walls. For an interpretation of the current distribution results, the method of integral relations in a linear approximation was used to solve the problem of a constant-velocity flow of a gas with variable electrical conductivity across a magnetic field in a plane magnetogasdynamic channel of constant cross section formed by electrodes of finite length and insulators. The Hall effect was taken into account. Experiments in which the effect of an external magnetic field on the current distribution on plane sectioned short electrodes in a magnetogasdynamic accelerator was investigated were described in [1]. In the present investigation, continuous long electrodes were used. These electrodes prevented the side effects due to coupling of the current to the ends of the electrode sections and helped to reveal some features of the current density distribution on the anode.

Effect of the form of the electrodes on the current distribution in a magnetogasdynamic channel

A solution is given to the plane problem of the flow of a conducting gas across a homogeneous magnetic field in a magnetogasdynamic channel taking account of the Hall effect at small magnetic Reynolds numbers. The channel is formed by two long electrodes, and the cross section of the channel varies slightly and periodically along the gas flow. It is assumed that the electromagnetic forces are small. It is shown that the current distribution in the channel is nonuniform to a consider able degree and that inverse currents can form at the electrodes, with both subsonic and supersonic flows of the conducting gas. Transverse motion of the gas, due to a change in the cross section of the channel, leads to an increase of Joule energy losses. In [1] the current distribution was obtained in a flat channel formed by infinite dielectric walls, with the flow of a steady-state stream of plasma through the channel across a homogeneous magnetic field. With interaction between the flow and the magnetic field, closed current loops develop in the channel.

Calculation of shock wave propagation in a magnetogasdynamic channel

Calculation of shock wave propagation in a magnetogasdynamic channel

Shock stability in magnetogasdynamic channel flows

The question of shock stability in a perfect-gas channel flow was examined in [1] in the onedimensional approximation under various assumptions: the disturbances are not reflected from the channel exit section, weak shock, etc. The results were found to coincide for two specific forms of the boundary conditions at the channel exit, from which it was concluded that the shock was not sensitive to the exit boundary condition. In [2] the question of shock stability was studied numerically in relation to a conducting-gas flow in a flat channel of constant cross section in the presence of a magnetic field (zero electric field intensity). It was established that the shock stability is significantly affected by the form of the conductivity law. A condition for the limiting regime between the stable and unstable regions was also given for flow with a shock wave. It was assumed that the pressure in the channel exit section is given. In this paper the effect of the exit boundary condition on shock stability in gasdynamic and magnetogasdynamic flows is demonstrated for small magnetic Reynolds numbers. Stability criteria are obtained for shocks near the channel exit for a specific exit condition. The influence of electromagnetic effects (conductivity law, electric load factor) on shock stability is investigated.

Magnetogasdynamic channel flows

The asymptotic behavior of small unsteady perturbations that are superposed on an equilibrium magnetogasdynamic channel flow is considered. Only those channels with slowly varying cross-sectional area and small characteristic width-to-length ratio are allowed, so that variations along the channel are typically much smaller than are those across the channel. Under these conditions and the provision that the current density inside the duct is small, a set of quasi-one-dimensional equations is obtained. From the resulting set of hyperbolic equations, the theory of characteristics provides certain compatibility relations that describe the behavior of small disturbances of the steady channel flow, which are caused by some local pressure fluctuation. Two distinct wave motions are present within the channel, and the asymptotic behaviors of both are examined with the use of the aforementioned compatibility relations. It is shown that, under certain conditions on the magnetic-field distribution, wave motions that lead to shock formation in ordinary gasdynamic flow will attenuate because of the action of the magnetic field. Therefore, an instability is no longer predicted, and the possibility of a stable or shockless flow, due to the action of a suitably placed magnetic field, is revealed. a A B c d E H h 3 Mc p p

Nonuniformities in Magnetogasdynamic Channel Flow

On the Entropy Change Through a Shock Layer JAMES SERRIN AND Y. C. WHANG 990 T QUASI-ONE-DIMENSIONAL magnetogasdynamic channel flow equations have been presented for the case of mutually perpendicular applied electric and magnetic fields. As it was later pointed out, the flow variables-—e.g., pressure, velocity, current, magnetic field, electromagnetic body force, etc.—are to be taken as average values, and the need for Maxwell's equations arises only in evaluating the induced part of the magnetic field by means of the Biot-Savart law. This induced field is then subtracted from the total field used in the channel-flow solution, in order to ascertain the field to be applied at each position. Following the indicated calculation, the resulting expressions for the x and z components of the induced field are seen to exhibit a dependence not only on position, but on channel height, a, width, b, and length, L. The notation is that of Ref. 2 with x indicating the flow direction.

Linearized Magnetogasdynamic Channel Flow With Axial Symmetry

Linearized Magnetogasdynamic Channel Flow With Axial Symmetry

Similar Solutions for Boundary Layers in Constant-Temperature Magneto-Gasdynamic Channel Flow

One of the problems that must be faced in the development of plasma accelerators is the growth of boundary layers upon the accelerator walls. The boundary-layer effects may be important not only from a heat-transfer standpoint, but because of the displacement effect on the main flow. For the steady-flow accelerator utilizing crossed electric and magnetic fields, such as that discussed by Resler and Sears, a very interesting situation may develop upon the walls that are perpendicular to the current flow. Since the wall must generally be cool, there is a tendency for the plasma conductivity near the wall to be lower than that in the relatively hot free stream. Consequently, the Joule heating associated with the continuous current will be highest in the neighborhood of the wall. This increased heating may produce an abnormal thermal boundary layer and, quite possibly, a severe heat-transfer condition.