An actuator-disk model for azimuthally nonuniform MPD arcs.

Recent experiments have shown that, under some conditions of operation, the current pattern in an MPD arc is azimuthally nonuniform and rotates with a constant angular velocity, which increases with current and applied magnetic field but decreases with propellant mass flow rate. A model for such a flow is proposed which is based on the physical assumption that the current flows in a single column and upon the mathematical assumption that azimuthal averages of mass, momentum, and energy fluxes are time-in variant. The model is thus analogous to the actuator disk model, which describes the flow induced by a propeller. Additional hypotheses are made concerning flow properties and arc motion which are based on a limited experimental and theoretical understanding of magnetically balanced arc columns. A dimensionless correlation of all existing experimental measurements is derived and a criterion for the existence of current spokes is suggested.