Feasibility Study of Magnetohydrodynamics Acceleration of Unseeded and Seeded Airflows

Nonequilibrium, reacting, ionized gas flow modeling is used to study the feasibility of magnetohydrodynamics (MHD) acceleration of airflows for the energy addition wind tunnel. The kinetic model incorporates equations of one-dimensional magnetogasdynamics, the master equation for vibrational level populations of diatomic species, equations of chemical and ionization kinetics, and the Boltzmann equation for electrons. The model is validated by comparison with the experiments in MHD accelerators. Calculations are made for two accelerator schemes, the first using an electron beam to sustain nonequilibrium ionization in unseeded air and the second using alkali-seeded air. Although at low pressures external ionization allows substantial increase of the flow total enthalpy, the obtained test section pressure is much lower than required, and the flow quality is poor. Calculations for alkali-seeded flows predict test section flow parameters closer to the target values, with O atom and NO concentrations lower than in the e-beam-controlled flows. Flow stability is analyzed using the linear stability theory. A thermodynamic energy addition criterion is used to demonstrate the advantage of direct kinetic energy increase in MHD acceleration over thermal energy addition methods