Experimental and theoretical studies of the effects of nonuniformities in equilibrium magnetohydrodynamic flows

Abstract

An experimental study of the effects of thermal and velocity nonuniformities is performed in an equilibrium plasma for a range of Hall coefficients. By introducing equally spaced cold blades in the radial flow of an electrodeless magnetohydrodynamic disk deivce, it is possible to create well-defined two-dimensional wake nonuniformities with strong variations of the plasma properties in the direction normal to the magnetic field and the flow. This type of nonuniformity and orientation theoretically provides the strongest reduction of Hall coefficient and effective conductivity for high values of the Hall coefficient. This degradation which reached more than 50% in some cases, is controlled by both the level of nonuniformities and the value of the ideal Hall coefficient. The former is dependent upon the number of blades (root mean square deviation of the conductivity), and the latter is dependent upon the values of the magnetic field intensities. The results provide basic quantitative information about the effects of conductivity and velocity nonuniformities on the performance of equilibrium magnetohydrodynamic generators over a wide range of Hall coefficients. The theoretical predictions are derived from a detailed two-dimensional electrodynamic analysis and a simplified engineering model based on a generalization of Rosa’s layer model. These experiments validate the analytical studies and support the use of the theoretical layer nonuniform models in describing the effect of boundary layers on the performance of linear magnetohydrodynamic devices.