Abstract
Two-dimensional stability analyses for open-cycle supersonic disk MHD generators are carried out which take into account electrical boundary conditions. A method of γ-θ two-dimensional linear stability analysis for 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. Whether the perturbations grow or decay is judged diagramatically in a way similar to the Nyquist's method. A coal-fired outflow supersonic disk MHD generator of commercial scale is analyzed under several types of boundary conditions. The stability is much affected by the electrical boundary condition and also by the azimuthal wavenumber of disturbance. The two-dimensional analysis has revealed an azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the one-dimensional analysis. The analysis also shows that the instability can be suppressed by subdividing the load section with some control electrodes.
