A detailed numerical model has been developed to study the gasdynamic flow in an electrothermal arcjet thruster. This two-temperature, Navier-Stokes model consistently incorporates viscosity, heat conduction, ohmic dissipation, collisional energy transfer between electrons and heavy species, ambipolar diffusion, nonequilibrium dissociation and ionization, and radiation. The fluid equations are solved by MacCormack's method while an iterative procedure is used to relax an electric potential equation, from which the current distribution in the thruster is obtained. Using hydrogen propellant, solutions are achieved for a range of input parameters and the underlying physics and internal structures of these arcjet flows are revealed. In particular, a mechanism for self-sustaining anodic arc attachment is identified. It is found that ambipolar diffusion from the arc core coupled with enhanced nonequilibrium dissociation and ionization in the outer flow provide enough charge carriers for the current to pass self-consistently between the arc core and the anode wall. Numerical solutions are compared with experimental results from the German TT1 radiatively-cooled arcjet thruster. Calculated discharge voltage is within 1-2% to 10% of experimental measurements, and predicted specific impulse is within 5-10% agreement over a range of applied currents and mass flow rates. In addition, flow solutions are used to explain observed trends in performance as quantities such as the specific power and mass flow rate are varied. An anode thermal model is constructed which yields more accurate predictions of the inlet gas and electrode wall temperatures, and this model is coupled to the arcjet flow solver in order to obtain a more self-consistent solution. Finally, a simplified stability analysis of the near-anode arc attachment region is performed. It is found that a localized ionization instability may be initiated in this region, but that the system is stable under the flow conditions predicted by the arcjet simulation of this research. (Copies available exclusively from MIT Libraries, Rm 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).
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