SELF-SIMILAR DEVELOPMENT OF INVISID HYPERSONIC FREE-JET FLOWS.
LOCKHEED MISSILES AND SPACE CO SUNNYVALE CALIF
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The steady, inviscid, free expansion of a jet from a sonic orifice into a vacuum passes into an inertia-dominated regime that has very nearly radial streamlines and selfsimilar flow-property profiles beginning not far from the orifice and extending outward to infinity. If there is a low but finite counter-pressure at infinity, the inertia-dominated flow field extends out to the shock system imposed by the counter-pressure. The possibility of radial, selfsimilar flow is deduced from a simple analysis, and the form of the self-similar density profile is deduced for gamma 53, 75, and 97 by reference to numerical calculations by the method of characteristics. A simple analytic fitting formula is obtained which is numerically accurate in the hypersonic regions of the jet and provides a much more convenient description of this flow region than is given by the method of characteristics. Since the key assumption of the analysis is that the flow speed is very close to a constant adiabatic limit speed, the similarity seems to be limited to flows of perfect gases, or to real gases with frozen internal degrees of freedom. Author