Supersonic acoustic source mechanisms for free jets of various geometries

The aeroacoustic performance of several generic nozzle geometries was tested to evaluate the potential benefits of using non-round jet exit geometries to reduce noise from combat military aircraft. Both the aerodynamics and far field acoustics of several M(sub d) = 1.5 and 2.0 round, elliptic, and rectangular nozzles, including an augmented deflector exhaust nozzle (ADEN), were studied to assess noise emission. The nozzles were operated to jet total temperatures, T(sub 0) = 1160 degree R, and the data scaled to constant thrust. The data were propagated to 1500 ft. and corrected to perceived noise level. The aerodynamic results of the study show that the non-round nozzle geometries mix much faster with the surrounding medium than does an equivalent round nozzle plume. Both the ADEN and elliptic nozzles provide significant reduction of noise, 6 to 7 PNdB, along the major axis direction with little expected impact on nozzle performance. Shock noise processes are eliminated for elliptic nozzles, but are still significant with rectangular nozzles. Comparison of measurements to theoretical predictions of noise using the quasi-linear instability wave model demonstrates good qualitative agreement.