MHD Flow Behavior and Performance of Subsonic Non-equilibrium Disk MHD Generator Driven by Shock-tube Facility.

Abstract

MHD flow behavior and the performance of an experimental nonequilibrium subsonic disk MHD generator driven by a shock-tube facility have been examined with time-dependent γ-z two-dimensional and γ-θ-z three-dimensional numerical simulations. In the subsonic MHD generator with two throats, the choking position is found to depend on the strength of MHD interaction. For optimal or high load operations, the flow chokes at the downstream throat and the subsonic flow is maintained in the generator channel. For low load operations, on the other hand, the flow chokes at the upstream throat and the flow becomes supersonic. In the generator under the subsonic flow condition, the relation between enthalpy extraction ratio and isentropic efficiency can be described as a function of Mach number at the anode for a fixed Mach number at the cathode. When the magnetic flux density is low, the inlet stagnation pressure should be decreased to achieve high enthaply extraction ratio and isentropic efficiency. The proper fluid flow and discharge structure can be realized under the optimal load resistance. Under the low resistance, however, shock-waves and ionization instability can occur and the generator performance can be deteriolated.