We investigate the feasibility of using Magneto-Hydrodynamics (MHD) to implement a propeller-less propulsion system. The basic principle behind MHD is to use the (Lorentz) force produced by the interaction of electric and magnetic fields to generate thrust on a conducting fluid in motion. Electrodes are lined up along the walls of the duct which act as the source of the electric field. Sea-water acts as the conducting medium for the current when it passes through the duct. This medium is then subjected to a strong magnetic field within the duct, thereby producing an axial force, i.e. an axial thrust. Propulsion systems based on MHD require virtually no mechanical components; therefore, a good application would be to design a propulsor which produces very little noise for small underwater vehicles. Results of a preliminary feasibility study on this application are presented in this paper. An approximate, consistent model to estimate the propulsion performance of a MHD propulsor for small underwater vehicles is introduced and analyzed. The model is generalized from the hydrodynamic point of view to consider inlet and outlet convergent/divergent nozzles. The general model is applied systematically varying the main design parameters considering a small autonomous underwater vehicle (AUV). Results show that non trivial trade-off conditions exist between inlet and outlet geometry, number of MHD channels, applied magnetic field and voltage, as the vehicle speed changes, to get the highest propulsion efficiency.

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