Electrode sheaths and boundary layers in hypersonic MHD channels

Hypersonic MHD channels in cold air, if developed, could allow, among other applications, the generation of power on board high-speed aircraft and the construction of hypersonic wind tunnels. The nonequilibrium conductivity in those channels has to be generated by external sources, such as electron beams, and very strong magnetic fields are required. The present paper analyzes near-electrode sheaths and boundary layers in cold hypersonic MHD channels, and both sheaths and boundary layers are revealed to be dramatically different from those in conventional systems. The reduced electron mobility across the magnetic field lines results in anomalously large anode voltage fall and in very thick anode and cathode sheaths. The very thick sheaths affect fluid and thermal boundary layers, and reduced density and high temperature in the boundary layers, in turn, affect the sheaths. Ponderomotive j x B forces are shown to significantly change effective viscosity, thus narrowing or widening the boundary layer, and affecting its temperature.