| Simulations of two self-field and one applied-field steady state magnetoplasmadynamic (MPD) thrusters were performed by the time-dependent, two-dimensional axisymmetric, magnetohydrodynamic (MHD) numerical code, MACH2. Substantial modifications were made to the code to include real viscous effects with viscosity and thermal conductivity models applicable to partially ionized gases. Also, steady state poloidal magnetic field boundary conditions that encompass the field's evolution in response to induced azimuthal plasma currents and time-varying external solenoidal fields were added.;Calculations of overall performance characteristics were compared to experimental data and exhibited excellent agreement of thrust and current distribution for the self-field thrusters. Voltage predictions, offset by estimates of electrode fall voltages, captured the experimental trends. Thrust predictions for the applied-field thruster captured the observed, nearly linear increase with applied magnetic field and discharge current, but underestimated the experiment. The dependence of plasma voltage on applied magnetic field strength was predicted, the dependence on discharge current however, was overestimated.;Interrogation of the calculated flowfield properties a new visualization of the applied-field MPD thruster operation, comprising the following elements: (a) The back electromotive force is the dominant contributor to the plasma voltage. (b) Viscous forces oppose applied azimuthal electromagnetic forces so as to limit the maximum rotational speed to a constant independent of field or current value. (c) Viscous heating provides the main acceleration mechanism which is conversion of thermal energy to axial directed kinetic energy. (d) The low density, low conductivity plasma does not adequately interact with the applied field in the manner of a so called magnetic nozzle. These lead to simple analytic expressions that predict the behavior and magnitudes of the thrust and voltage. |
PDF Full Text Request