T. A. Lapushkina

Influence of electric and magnetic fields on the shock wave configuration at the diffuser inlet

The possibility is investigated of influencing the shock wave configuration in a xenon plasma flow at the inlet of a supersonic diffuser by applying electric and magnetic fields. Flow patterns resulting from interaction of the plasma with external fields in the entire diffusor volume and its different sections are compared. The patterns are obtained by the Schlieren method using two recording regimes: individual frames or a succession of frames. The study focuses on the normal shock wave formation process under strong MHD interaction over the whole diffuser volume. Basic factors affecting the plasma flow velocity in the diffuser under externally applied fields are compared, namely, the ponderomotive force and the Joule heating of the gas by the electric field, which decelerate the supersonic flow, and the heat removal to the external electric circuit producing the opposite effect. It has been shown that the external fields are most effective if applied to the inlet part of the diffuser, while the flow in the diffuser section, where there is a large density of dissipative structures, is not readily responsive to external factors. It is suggested that the measure of response can be estimated by the energy that goes to the shock wave formation as a result of the flow interaction with the diffuser walls.

The effect of MHD interactions on the input shock waves in a supersonic diffuser

The interaction with an external magnetic field modifies the variation of the shock wave configuration in a pure inert gas plasma at the entrance of a supersonic diffuser. The phenomenon was studied using an experimental setup based on a shock tube with a flat nozzle and the model supersonic diffuser. The experiments were conducted in krypton, for the shock wave Mach number in the shock tube M=7.8 and the Mach number at the nozzle exit M=4.2. The gasodynamic discontinuities and their structural variations induced by the magnetic induction changes were by visualized by the schlieren method and by photography of the intrinsic emission accompanying the process. Three regions of the MHD interaction affecting the shock wave configuration in the gas flow were revealed.

Supersonic flow of a nonequilibrium gas-discharge plasma around a body

The flow of a nonequilibrium gas-discharge plasma around a semicylindrical body is studied. The aim of the study is to see how a change in the degree of nonequilibrium of the incoming plasma changes the separation distance between a shock wave and the body. Experiments are carried out with a supersonic nozzle into which a semicylindrical body is placed. The inlet of the nozzle is connected to a shock tube. In the course of the experiment, electrodes built into the wall of the nozzle initiate a gas discharge in front of the body to produce an additional nonequilibrium ionization in the stationary incoming supersonic flow. The discharge parameters are selected such that the discharge raises the electron temperature and still minimizes heating of the gas. The degree of nonequilibrium of the flow varies with gas-discharge current. Diagnostics of the flow is carried out with a schlieren system based on a semiconductor laser. The system can record flow patterns at definite time instants after discharge initiation.

Characteristics of a magnetogasdynamic diffuser under different modes of electric current switching

This paper elaborates upon a previous investigation into the influence of external electric and magnetic fields on a flow through a supersonic diffuser. The aim of the present study is to correlate a change in the configuration of a shock wave emerging near the diffuser inlet at magnetohydrodynamic interaction with the amount of force and energy actions and with total pressure losses. For this purpose, the main parameters of the shock wave structure and the total pressure are measured at the diffuser outlet when the flow is subjected to magnetic and electric fields of various strengths at different routes of current passage. In the experiments, a shock tube with a supersonic nozzle is employed. The shock tube forms a flow behind the shock wave reflecting from the end of the tube, which terminates in the nozzle. The diffuser is located directly downstream of the nozzle. The investigation is carried out in xenon. The flow is subjected to external fields at the inlet of the diffuser. The shock wave structure is visualized by frame sweeping of Schlieren patterns of the flow. The total pressure is measured with a piezoelectric transducer located at the end of the channel. The results obtained make it possible to optimize the action on the flow in terms of power consumption and total pressure losses for a given design of the diffuser.

Supersonic flow about a body exposed to electric and magnetic fields

The feasibility of using nonmechanical (electrogasdynamic, EGD, and magnetohydrodynamic, MHD) methods to control shock-wave configurations emerging in supersonic flows is investigated. In the EGD method, the flow is heated by a gas discharge; in the MHD one, the flow is influenced by a Lorentz force arising in a gas discharge upon applying a magnetic field. The influence of the gas discharge and MHD interaction on the position of a detached shock wave appearing in a supersonic xenon flow about a semicylindrical body is studied. A discharge is initiated in the immediate vicinity of the leading edge of the body, and the variation of the shock wave position with the intensity of the discharge (discharge current density) is traced when the influence of the EGD action increases and/or an external magnetic field is applied (the influence of the MHD action increases). Preliminary data for a supersonic air flow about a body are presented.

Investigation of a Hall MHD channel with an ionization-unstable plasma of inert gases

We investigate a promising scheme for using ionization-unstable plasmas of pure inert gases as the working medium for a magnetohydrodynamic (MHD) closed-cycle generator. Our experiments were carried out using a disc Hall MHD channel, with the flux of ionized gas created in a shock tube. Our working gas was xenon. In these experiments we measured the gas pressure, the flow velocity, the concentration and temperature of the electrons, the azimuthal current density, the distribution of potential in the channel, and the value of the near-electrode voltage drop. We recorded voltage-current characteristics for various values of magnetic field and load resistances. The results of these experiment showed that in an ionization-unstable plasma of inert gases without admixtures of alkali metal, the effective conductivity in the Hall channel increases significantly with increasing degree of criticality of the magnetic field, and the value of the maximum specific power extracted increases more rapidly than the specific power calculated by assuming “frozen” ionization.

Investigation of Nonequilibrium Gas Discharge Plasma Supersonic Flow Around Body

In the work features of the flow around half cylindrical body by nonequvibrium gas discharge xenon plasma with purpose to investigate changes of the bow shock wave shift with changes of the incoming plasma nonequvibrium degree, that is with change of ratio the electron temperature to the temperature of heavy component. Investigations are carried out in supersonic nozzle where half cylindrical body was place. Nozzle inlet connects with shock tube. In the process of stationary streamline before body gas discharge is switched on by means of electrodes built-in nozzle walls. Discharge parameters were chosen so that to increase electron temperature but to minimize joule heating of gas. Flow nonequvibrium degree was changed by means of value changes of gas discharge current. Flow diagnostic was made by means of Schlieren system on the base of semiconductor laser allowed to create streamline pictures at the appointed time moments after discharge. Electron temperature was obtained from experiment, gas temperature was taken from calculation.

Relaxation of the shock-wave configuration in a diffuser after termination of the action of magnetic and electric fields

The pulsed interaction of an ionized gas flow in a full-internal-compression diffuser with magnetic and electric fields has been experimentally studied. The interaction is determined by the shape of the electric current pulse between electrodes situated in the initial part of a hypersonic diffuser. It is established that, after termination of the current pulse, some characteristics of the shock wave front configuration in the gas flow exhibit relaxation with a significant delay to the unperturbed values.

Recent Results On MHD Flow Control At Ioffe Institute

§§ This paper is a review of the investigations carried out at the Ioffe Physico-Technical Institute in collaboration with the Johns Hopkins University under the support of the EOARD during 2001 – 2006 years. These investigations were devoted to searching for ways and means of affecting a supersonic flow of a weakly ionized gas by an electromagnetic impact aimed at the magnetohydrodynamic (MHD) control of gas flows. In the course of the experimental investigations the authors were studying magnetohydrodynamic processes in supersonic xenon and nitrogen flows over plane models affected by external electric and magnetic fields, and, at the latest stage, about a body of revolution containing all components of the electromagnetic system inside itself. The results obtained evidence possibilities of an effective control of the shock wave structure of supersonic gas flows by MHD method. Also first attempts to measure heat flux toward the body surface under the interaction were made. Some initial results of measurements of the heat flux are presented.

Local effect of electric and magnetic fields on the position of an attached shock in a supersonic diffuser

Effective ways for controlling shock wave configurations by means of external actions are sought. One such way is a local effect of electric and magnetic fields. In this paper, the local effect of external fields is implemented by current localization in a limited region of a diffuser. The experiment is carried out in a diffuser providing the complete internal compression of the gas with a Mach number at the inlet M=4.3. As a working medium, a xenon plasma is used. The plasma flow is formed in a shock tube equipped with an accelerating nozzle. Two ways of current localization are tested. In the first one, the diffuser inlet is a short channel of Faraday generator type. In this case, the ponderomotive force basically decelerates or accelerates the flow depending on the direction of the electric field. In the second way, the current flows through a narrow near-wall region between adjacent electrodes. In this case, the ponderomotive force compresses or expands the gas. In both cases, it is shown that the angle of an attached shock due to MHD interaction can be both decreased and increased. The central problem with the MHD control of shock waves is near-electrode and near-wall phenomena.