Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

The importance of jet noise for prospective supersonic transport (SST) in takeoff and climb modes dictates the need to develop methods for reducing jet noise and their subsequent validation in large- and full-scale tests. This paper presents the results of Russia’s first ground acoustic tests of a rectangular nozzle with a noise suppression system, installed on a subsonic aircraft engine to demonstrate the technology. The authors studied a rectangular beveled nozzle with an ejector and screens—elements of the SST airframe. The test results were compared for three nozzle geometries: a round nozzle corresponding to measurements for the original engine without modifications, a rectangular nozzle without screens, and a rectangular nozzle with screens. It was found that when the rectangular nozzle without screens is used, there two opposite effects occur: noise amplification compared to the round nozzle for angles of observation close to the jet axis, and noise attenuation at angles of observation close to the fan rotation plane. Installing screens increases noise up to 5 dB in the low-frequency region below 150 Hz and reduces noise by 2 dB for frequencies higher than 250 Hz. Estimation of community noise in the EPNL metric showed that this rectangular nozzle with the noise suppression system has the effect of reducing community noise in comparison with the baseline round nozzle.