Separation of Gas Mixtures in Supersonic Jets

The supersonic jets resulting from the free expansion of nitrogen—hydrogen mixtures from small sonic nozzles were carefully studied by means of pressure and composition probing. The apparent concentration of heavy species in the core of the jet, originally observed by others, was confirmed. The mechanism by which this separation occurs is shown to be a consequence of the presence of the probe. The deceleration occasioned by the bow shock on the probe is suggested as the cause of the separation. The previously suggested mechanism of radial migration of light species from the jet axis does not seem to be applicable to the present results.