Propulsive Efficiencies of Magnetohydrodynamic Propulsors Considering Electrical and Magnetic End Effects

Abstract : A mathematical theory for the performance of a direct current, rectangular duct magnetohydrodynamic (MHD) propulsion system propelling a marine vehicle is presented. The model accounts for the effects of spatially nonuniform magnetic fields and current distributions which are present at the ends of the propulsion unit. The theory is based on an approximate solution of the general NM duct flow problem in which the mutual interaction of the electric current and fluid flow in a strong magnetic field are considered in detail. For a specified vehicular steady state cruising speed, the propulsive efficiency and electrical power requirements can be calculated from the theory given the hydrodynamic drag of the vehicle and the properties of the fluid medium. Explicit electrical end loss factors are calculated to relate the performance of a propulsor with nonuniform field distributions to the performance of an idealized propulsor with no end losses operating under the same conditions. The power losses due to auxiliary equipment such as electrical generators, buswork, and magnetic cryogenic systems are not included in the study. Numerical results from the models for five design configurations for a nominal geometry under a reasonable range of operating parameters are presented. The numerical results, including the ideal propulsor with no end effects, indicate that the fringing magnetic and current distributions at the ends of the duct generally significantly degrade the propulsive efficiency. The degree of degradation depends on details of the design configuration of the rectangular duct.