Two-dimensional linear stability analysis of coal-fired disk MHD generator

Abstract

Two-dimensional stability analyses are carried out for open-cycle disk MHD generators, where their electrical and gasdynamic boundary conditions are considered. First, a method of r-theta 2-D linear stability analysis for a supersonic disk MHD generator is proposed which examines the time growth rate of perturbations. The growth rate is determined by the characteristic equation which is derived from the electrical boundary condition. A coal-fired outflow supersonic disk MHD generator is analyzed under several types of boundary conditions. The 2-D analysis has revealed azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the 1-D analysis. Next, a method of 2-D linear stability analysis for a subsonic disk MHD generator is proposed which requires the gasdynamic boundary condition as well as the electrical boundary condition. A coal-fired inflow subsonic disk MHD generator is analyzed under several types of boundary conditions. It has been found that some gasdynamic boundary conditions develop 2-D instability although they do not cause 1-D instability. (Author)