Acoustics Measurements of Scale Models of Military Style Supersonic Beveled Nozzle Jets

The emergence of louder, more powerful fighter aircraft has caused the research of supersonic jet noise reduction devices. Noise emitted towards the ground is most important during the takeoff segment of the flight profile (when the jet exhaust flow is typically over expanded). Small scale measurements are important so that noise reduction concepts can be evaluated early in the design process. In the past, acoustic measurements from the heat simulated small-scale anechoic facility at PSU have been compared to acoustic measurements from larger scale heated anechoic facilities with excellent results. Beveled exits for subsonic nozzles rotate the jet plume and primarily reduce noise through the subsequent rotation of the acoustic field. Until recently, this was believed to be the case for beveled exits on supersonic convergingdiverging nozzles. The jet plume from such nozzles was examined and shown to deflect less than 6 degrees for both over-expanded and under-expanded flows. Therefore any measured noise reduction is due to the alteration of the noise generation mechanisms and not the deflection of the jet plume. Beveled nozzles with the exit plane rotated 24 and 35 degrees were tested along with a baseline nozzle. Results show that for heated jets, noise in the peak emission direction was reduced by 3-4 dB on the long lip side of the nozzle, with very little altercation to the short lip side. For over expanded flows there was very little gain or reduction in the sideline broadband shock associated noise (BBSAN). However, for nearly perfectly expanded heated jets there was a noticeable increase in the sideline noise for the high frequency BBSAN.