A new blowdown nonequilibrium plasma magnetohydrodynamic (MHD) supersonic wind tunnel operated at complete steady state has been developed and tested at Ohio State. The wind tunnel can be operated at Mach numbers up to M = 3-4 and mass flow rates of up to 45 g/s at a stagnation pressure of 1 atm. Pitot tube and schlieren measurements in a M = 3 test section showed reasonably good flow quality, up to 80% inviscid core across the larger dimension and up to 50% inviscid core across the smaller dimension of the flow. Stable and diffuse transverse rf discharges (rf power up to 1 kW) have been sustained in M = 3 nitrogen flows, at magnetic fields of up to B = 1.5 T. Operation at higher magnetic fields produced a more uniform rf plasma in the MHD test section. Hall parameter and electric conductivity of the flow have been inferred from the dc (MHD) current and voltage measurements at different values of the magnetic field. At B = 1.5 T and rf power of 500 W, the Hall parameter is β ∼ = 3 and the conductivity is σ ∼ = 0.05 mho/m. At the rf power of 1 kW, the extrapolated conductivity is ∼0.1 mho/m. The results of the present work demonstrate the Lorentz force effect on the supersonic boundary layer in M = 3 flows of nitrogen ionized by a high-power transverse rf discharge in the presence of the magnetic field. Boundary-layer density fluctuation spectra are measured using the laser-differential-interferometry diagnostics. In particular, decelerating Lorentz force applied to the flow produces a well-reproduced increase of the density fluctuation intensity by up to 10-20% (1-2 dB), compared to the accelerating force of the same magnitude applied to the same flow. The effect is produced for two possible combinations of the magnetic field and MHD current directions producing the same Lorentz force direction (both for accelerating and decelerating force). The effect is observed to increase with the flow conductivity. On the other hand, the effect of Joule heating on the density fluctuation spectra appears insignificant.

An approximate solution is devised for the one-dimensional motion following the impact of a shock wave on a wall which is free to move. The approximate solution neglects changes in entropy occurring through the reflected and transmitted shocks, thus reducing the problem to one of a simple wave type. The asymptotic behaviour of the system is considered and it is shown by exact physical argument that the transmitted shock eventually attains the same strength as the incident shock and that the reflected shock ultimately decays to a sound wave.An experimental investigation of the interaction was made, using thin walls of cellulose acetate, in a shock tube at an incident shock Mach number of 1·50. Agreement between the theoretical and experimental results, especially for the path followed by the wall, was found to be good.

No abstract

No abstract

An experimental study of shock modi cation in an M = 2:5 supersonic ow of nonequilibrium plasma over a cone is discussed. The experiments are conducted in a nonequilibrium plasma supersonic wind tunnel. Recent experiments at the Ohio State University using a supersonic plasma ow over a quasi-two-dimensional wedge showed that an oblique shock can be considerably weakened by a transverse rf discharge plasma. The previously observed shock weakening, however, has been found consistent with a temperature rise in the boundary layers heated by the discharge. In the present study, the boundary-layereffects on the shock wave are reduced by placing an entire cone model into a supersonic inviscid core ow. The electron density in the supersonic plasma ow in the test section is measured using microwave attenuation. The ionization fraction in the discharge is in the same range as in the previous plasma shock experiments, up to n e /N = (1.2-3.0) £ £ 10 ¡7 . The results do not show any detectable shock weakening by the plasma. This strongly suggests that the previously observed shock weakening and dispersion in nonequilibrium plasmas are entirely due to thermal effects.