Thermophysical and transport properties of multicomponent gas plasmas at multiple temperatures

D of MHD generator channels, in particular of the diagonally connected type, with appreciable Hall currents Jx (of the order of 1 A/cm) and with appreciable diameters (of the order of 1 m) must give special attention to the transverse flow asymmetries that develop inside the channel due to the pressure gradient normal to the electrode walls that is induced by the presence of Hall currents. In the present work, the compressible turbulent flow of seeded plasma in MHD channels is analyzed by a two-dimensional formulation that solves the equations of motion (including the ymo men turn equation) by an implicit finite difference scheme. The numerical method solves for all the unknowns, including the gasdynamic pressure and pressure gradient, across the channel at every numerical step taken in the streamwise direction. The present work will show that the Hall current density component Jx, if sufficiently large, can cause asymmetries in the mean gas velocity profile and other gasdynamic profiles.

Two-Dimensional Flow inside MHD Ducts with Transverse Asymmetries

The integral method developed in a companion paper [Phys. Fluids 31, xxx (1988)] is extended and applied in this work, to include electromagnetic body forces. A nonequilibrium ionizing argon boundary layer in an electric rocket thruster known as a magnetoplasmadynamic (MPD) thruster is studied. The steady boundary layer flow of a two‐temperature plasma adjacent to the electrode in a self‐field MPD thruster is analyzed for both frozen (zero ionization rate) flow and nonequilibrium (finite ionization rate) flow. The free‐stream boundary conditions for this analysis are obtained from the results of an earlier quasi‐one‐dimensional nonequilibrium theory. The ionizing, two‐temperature, compressible boundary layer equations with electromagnetic effects are solved using momentum and energy integral methods. This integral method without any electromagnetic effects has been described in the companion paper [Phys. Fluids 31, xxx (1988)]. This enables an approximate calculation of the wall shear and the heat transfer to the electrode. The most significant result of the two‐temperature boundary layer theory presented herein is to show the strong dependence of the viscosity on the ionization slip (i.e., ionization fraction at the wall). This affects such relevant quantities as boundary layer thickness, wall shear, and wall heat flux, which in turn influence viscous drag and electrode erosion.The integral method developed in a companion paper [Phys. Fluids 31, xxx (1988)] is extended and applied in this work, to include electromagnetic body forces. A nonequilibrium ionizing argon boundary layer in an electric rocket thruster known as a magnetoplasmadynamic (MPD) thruster is studied. The steady boundary layer flow of a two‐temperature plasma adjacent to the electrode in a self‐field MPD thruster is analyzed for both frozen (zero ionization rate) flow and nonequilibrium (finite ionization rate) flow. The free‐stream boundary conditions for this analysis are obtained from the results of an earlier quasi‐one‐dimensional nonequilibrium theory. The ionizing, two‐temperature, compressible boundary layer equations with electromagnetic effects are solved using momentum and energy integral methods. This integral method without any electromagnetic effects has been described in the companion paper [Phys. Fluids 31, xxx (1988)]. This enables an approximate calculation of the wall shear and the heat transfe...

Electrode-adjacent boundary layer flow in magnetoplasmadynamic thrusters

Experimental measurements were performed of temperature and electron number density profiles on a laboratory-scale MHD generator. Comparisons between calculations from a two-dimensional theory and measurements for cases without current generally showed good agreement when the turbulence model properly accounted for the effects of freestream turbulence, although small discrepancies were observed between theory and experiments for the overall profile shape, Comparisons of experimental temperature profiles without current to profiles with current showed a marked temperature increase in the boundary layer due to Joule heating. The magnitude of the increase was well predicted by the two-dimensional boundary-layer theory. Measured temperature profiles with current and magnetic field did not agree with predictions. The predicted profile in the inner region of the boundary layer for a case with current and magnetic field was above a similar case without current, whereas measurements for anode boundary layers were below control profiles without current. A cathode boundary layer behaved oppositely to the anode boundary layers. Three-dimensional recirculation induced by nonuniformities in axial current could explain the discrepancies.

Joule heating effects in MHD generator boundary layers

MHD generator performance predictions require an accurate determination of the voltage losses in the channel; however, most techniques for determining these losses need substantial calculations and/or computer storage space. This paper proposes a simplified method for calculating the ohmic boundary layer contribution to the overall voltage losses. Voltage drop regions are discussed and a description of the turbulent boundary layer contribution is derived. Appropriate simplifying assumptions on the basic transport and MHD concepts are used to express the conductivity as a function of temperature only. Weighting functions for averaging the resistivity in turbulent boundary layers are determined and the nature of these functions is presented. Our results are compared with more precise descriptions and with experimental results.

A simplified technique for determining the boundary layer voltage loss in MHD generators

The compressible laminar and turbulent boundary-layer equations representing the fiow of cesium seeded argon plasma over successive segments of the cathode wall of an MHD channel were investigated and solved for both finite and intinite rates of reaction. The equations solved include the electron energy and the electron continuity equations as well as the usual global boundary-layer equations. The effects of finite rates of reaction and ambipolar diffusion are considered, and the inner boundary conditions for both the electron energy and the electron continuity equations are obtained by investigating a sheath analysis. The governing equations are solved using a finite-difference scheme without introducing a local similarity assumption. The finite rate results are considerably different from the infinite rate ones. The main reason is the ambipolar diffusion which depletes the electrons near the wall. No special problems have been found in the solution of the turbulent flow equations. This is due to the high mobility of electrons. (auth)

E. D. Doss

Papers

Influence of Segmentation and Ambipolar diffusion on MHD Nonequilibrium Boundary Layers