Strong MHD Interaction Research Articles

Investigation of Pulsed Electric Discharge in Hypersonic Air Flow and in Magnetic Field

The problem of local braking of a high-speed air flow (M = 6) using an electric discharge plasma in a magnetic field has been considered. The studies were carried out on an experimental MHD test rig based on a shock tube, at the end of the low pressure channel of which a Laval nozzle was placed with gas flowing into the Eiffel chamber. The discharge was initiated across the flow, between narrow electrodes, and across the magnetic field. It was shown that with increasing of the magnetic field the discharge is localized between the electrodes and then moved toward the flow as a result of strong MHD-interaction. At the same time the bow shock in front of MHD-interaction zone is observed. A comparison of the shock wave structures during the flow around the discharge on free electrodes, near the plate and in front of the blunt body has been shown.

Effect of Electric Discharges in Magnetic Field on Hypersonic Flow around Bodies

To investigate the possibilities of magnetohydrodynamic (MHD) effects on a hypersonic flow structure, it is necessary to ionize the gas flow. It is possible to create a local region of conductivity of the flow using electrical discharges under experimental conditions. The paper considers the MHD interaction of a high-speed air flow and electrical discharges (high-voltage pulse and high-frequency) in a homogeneous magnetic field when flowing around test models. It is shown that the use of discharges in a magnetic field makes it possible to significantly change the shock-wave structure of the flow near a streamlined surface: to change the angle of the oblique shock, to generate new shock, to transform attached oblique shock to the bow shock. Systematization of the obtained data on the value of the hydromagnetic interaction parameter S characterizing the strength character of the observed effects is performed. Thus, S < 0.05 corresponds to the weak MHD-interaction, S = 0,05–0,15 – moderate MHD-interaction, S > 0.15 – strong MHD-interaction.

Influence of inlet ionization degree on performance of seed‐free MHD generator

AbstractPower generating characteristics of seed‐free linear shaped Faraday type and disk shaped Hall type MHD generators are examined by two‐dimensional numerical simulation with changing the inlet ionization degree. A liner shaped Faraday type generator can get stable and high power output at high inlet ionization degree. The net enthalpy extraction ratio, however, is reduced owing to the increase in the required pre‐ionization power. At low inlet ionization degree, on the other hand, ionization instability occurs and the enthalpy extraction ratio decreases. A disk shaped Hall type generator can get high net enthalpy extraction ratio even at low inlet ionization degree under a low pre‐ionization power. The net enthalpy extraction ratio decreases for an excessive inlet ionization degree because of a strong MHD interaction.

Three-dimensional computation of magnetohydrodynamics in a weakly ionized plasma with strong MHD interaction

A large-scale pulsed MHD generator with an MHD channel of 4.5 m, having demonstrated the maximum electric power output of 510 MW, is studied numerically with a time-dependent three-dimensional analysis. It is shown that strong oblique shock waves are generated at a connection between the nozzle and insulating walls, traveling to the channel exit. The strong oblique shock waves cause fluctuations of gasdynamic quantities along the x-direction, resulting in a slight decrease of the Faraday current density. As a result, the strong oblique shock waves deteriorate slightly the generator performance. It is also shown that a strong pseudo-shock wave with a large boundary-layer separation is induced by the strong MHD interaction under the condition of a low channel voltage. The boundary-layer separation becomes large near the anode because of the strong Lorentz force in the y-direction attributed to the large Hall current. It is also shown that the cross-sectional secondary flow attributed to the Hall current on the y– z plane is not induced under the present conditions.

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.

Three-dimensional structures of MHD flow in a disk generator

Three-dimensional nonuniform plasmas and boundary layers have been studied numerically under an MHD interaction. The nonuniform plasma of "streamer" owing to weak ionization of seed material has a spiral structure in the r-/spl theta/ plane, and the plasma becomes almost uniform between the walls in the r-z plane. This structure is almost the same as that in our previous paper (1997), where the gas (heavy particle) properties are assumed to be invariant and steady. In addition to the streamer, the nonuniform plasma of "domain" owing to weak ionization of noble gas is revealed. The domain has the structure perpendicular to the streamer. In a strong MHD interaction case, the static pressure considerably increases in the upstream region of a generation channel, and the pseudo-shock waves appear in the generator, but the plasma is almost uniform along the /spl theta/ direction. The boundary layer in the strong MHD interaction is considerably thick, and in the broad region near the wall the Hall current flows reversely. In the weak MHD interaction case, the plasma forms a nonuniform structure along the /spl theta/ direction, and the Hall current does not always flow in the opposite direction even on the insulator wall since the azimuthal electric field is not zero.

High-Enthalpy Extraction Demonstration With Closed-Cycle Disk MHD Generators

Recent results of high-enthalpy extraction experiments with closed-cycle MHD disk generators are described. Power generation experiments were carried out with two types of facility: the shock tube facility with the Disk-IV generator and the FUJI-1 blow-down facility. In the shock tube experiments, the effect of channel shape on generator performance was studied using helium seeded with cesium as working fluid. A more divergent channel shape was effective in sustaining a high Hall field throughout the channel and achieving high generator performance even under the strong MHD interaction. High-enthalpy extraction of 27.3 percent was achieved. Furthermore, these experimental results agree well with the results of one-dimensional calculations. In the FUJI-1 blow-down experiments, the effect of stagnation gas pressure on performance was studied with a working gas of seeded argon. The highest enthalpy extraction ratio of 15.7 percent was achieved with the lower stagnation pressure of 0.46 MPa, whereas the largest output power of 516.7 kW and power density of 70 MW/m3 were extracted with the nominal stagnation pressure of 0.6 MPa. This suggested the possibility of a part-load operation without significant degradation of generator performance by reducing stagnation pressure.

Numerical simulation studies on FUJI-1 experiments

Experimental results of the FUJI-1 disk generator have been discussed from the calculated results based on the quasi-one-dimensional model. The calculations have been performed for generators with different channel shape to investigate the effects of the area ratio on power generation performance. The increase of output power at the high load resistance regime with increase of area ratio has been qualitatively shown by calculations, however absolute values of the plasma properties in an MHD channel obtained from the calculations have not been in agreement with experiment values. To clarify the pressure loss mechanism, the influences of the plasma properties on the changes of stagnation pressure have been investigated analytically. It has been found that the strong Lorentz force takes a significant role in the pressure loss processes as compared with wall friction under a strong MHD interaction conditions. Furthermore, it has been suggested that a 100 MW class thermal input generator is required to reduce the stagnation pressure loss by wall friction with high gas velocity and high output power.

Initial tests of a lightweight, self-excited MHD power generator

Data from the first seven power tests of a lightweight, self-excited MHD generator system are presented. Among the achievements of these tests were: 1) highest power from a diagonally connected MHD generator in the United States (4.8 MW, gross), 2) fastest self-excitation time for an MHD generator (0.4 s), and 3) highest specific power for a combustion-driven MHD generator in the United States on the basis of gross or net power per unit system mass. The tests show evidence of strong MHD interaction processes, including magnetoaerothermal effects, as expected from the design calculations. Solution of the intricate problems presented by these processes for each size of this family of MHD generators is necessary before the ultimate performance of these systems is realized. The software for obtaining these solutions has been validated, and some results are discussed in this paper.