MHD boundary layer of the seeded combustion gas near cold electrodes

Abstract

A theoretical analysis of the seeded combustion gas boundary layer near cold electrodes was made under the magnetic field, and the effects of the magnetic field on various physical quantities in the boundary layer and the stability of current discharge of diffuse mode were clarified. First, a boundary-layer analysis was done using a three-fluid model that considered the phenomena near cold electrodes such as charge separation, electron temperature elevation above gas temperature, and nonequilibrium of electron number density from the Saha equilibrium value for the electron temperature for both cases of a continuous Faraday electrode and an ideally segmented Faraday electrode. It was shown that, in the case of an ideally segmented Faraday electrode, the nonequilibrium of electron number density for the Saha equilibrium value for the electron temperature became larger due to the magnetic field in the laminar boundary layer; whereas, Saha equilibrium of electron number density for the electron temperature was almost established in the turbulent boundary layer of practical MHD generators. Next, in order to investigate the effect of the magnetic field on the critical value of discharge mode from diffuse to constricted mode, an analysis of a linear stability theory was applied for a simplified model where the electron number density was given by the Saha equilibrium value for the gas temperature, the steady value of which was assumed uniform in the thin layer very near the cold electrode. It was made clear that a perturbed propagating wave was generated, and that discharge of diffuse mode would become very unstable because of the magnetic field.