The flow field of a sonic jet exhausting counter to a supersonic airstream has been investigated theoretically and experimentally. The total shock-layer thickness was calculated using a blunt-bodytype analysis and the known properties of a free-jet expansion from a sonic orifice. The total shock-layer thickness and position of the outer shock relative to the orifice are shown to be a function of freestream Mach number, jet reservoir pressure, free-stream pitot pressure, and orifice size. The

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... dicted inner shock position is compared with previously published experimental data, and the predicted outer shock position is compared with data obtained in a low density wind tunnel. Results in the transitional flow regime indicate that the outer shock to orifice position distance is greater than the predicted value.