Interferometric Studies of Faster than Sound Phenomena. Part II. Analysis of Supersonic Air Jets

A study of supersonic air jets has been made by the use of the Mach interferometer. The density distribution in axially symmetric jets with several tank-receiver pressure ratios has been determined, with special emphasis on the 3.7-7 range of ratios. In terms of the dimensionless quantities $\frac{\rho }{{\rho }_0}$ (ratio of jet density to tank density) and $\frac{Z}{D}$ (ratio of distance from orifice to orifice diameter), all jets are closely the same in a region bounded by the orifice and an oblique line from the orifice edge. This line marks an inflection point in the streamlines, and probably indicates the low pressure termination of a three-dimensional Prandtl-Meyer expansion region which reduces the pressure at this point below that of the receiver. The strength of the stationary shock wave in general agrees with that predicted by the Rankine-Hugoniot equations. Recent theoretical computations of the density in the axis of the jets by Owen and Thornhill are in satisfactory agreement with the experimental results, but so far no suggestion has appeared for a theory to predict the three-shock configuration in jets.