Measurement of Shock-Wave Structure in Helium-Argon Mixtures

Abstract

Shock-wave density profiles have been measured for each component in helium-argon mixtures over the argon mole fraction range from 0.011 to 0.87. The shock waves were produced by a shock holder in the flow field near the exit of a Mach 2 nozzle. The species densities were derived from spectrally resolved measurements of the radiation from gas atoms excited by an electron beam. The measured species density ratios across the shock waves agreed within 7% with each other and with theory. Diffusive separation of the mixture was observed within the shock wave and the helium was compressed upstream of the argon in all cases. No initial acceleration of the argon was observed for small argon mole fractions contrary to the continuum calculations of Sherman. Diffusion effects resulted in considerable broadening of the shock wave, and for argon mole fractions of 0.1 to 0.2 the maximum-slope thickness of the mixture was almost three times the corresponding value for a pure gas.