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Flow Field and Acoustic Measurements of Rectangular Supersonic Jets

Acoustic and flow measurements from nozzles representative of modern military aircraft jet engines are scarce, due to the expense of making measurements with the full scale engines and the uncertainty in the accuracy of model scale measurements. The present study focuses on Pitot probe and acoustic measurements from jets issuing from a rectangular nozzle designed as a scaled model of a F-22 aircraft engine exhaust nozzle. Refined flow field measurements in supersonic under-, over- and fully expanded cold jets were performed with a Pitot probe and quantities such as the local Mach number and velocities were extracted. The presence of axis switching was observed from these, as well as the influence of the presence of shocks on the distance at which the switching occurs. Acoustic measurements in cold and heat-simulated jets issuing from the same nozzle were performed and showed a modest reduction in the measured sound levels for the rectangular jet. Addition of paddles similar to the thrust vectors from the real aircraft show additional reduction of the propagated sound levels.