Study of the insulating wall boundary layer in a Faraday MHD generator

Abstract

An experimental and analytical investigation of the insulating wall boundary layer in an operating MHD generator was undertaken. Velocity profiles were measured by a laser anemometer technique and the results compared with the finite difference solution of the momentum, energy, and electrical equations accounting for variable equilibrium properties. Both experimental and theoretical results showed a velocity overshoot near the wall for subsonic flow with an attendant increase in friction factor and Stanton number over that expected without MHD effects. The calculations were extended to larger size MHD generators; and for a subsonic pilot plant unit, an increase of the sidewall friction factor of over 150% was indicated with a 50% increase in Stanton number. Calculations for a supersonic generator showed that flow separation may occur on the sidewall because of the current pattern caused by the temperature overshoot common in supersonic boundary layers.