Abstract

It is understood that jet noise is an important noise source of future supersonic civil transport (SST) during takeoff and cutback regimes so that the development of SST jet-noise reduction methods is a necessary condition for compliance of the SST with the community noise regulations. Within the framework of investigation on the SST jet-noise reduction, the acoustic tests of a small-scale rectangular nozzle of the “mixer–ejector” type with a noise attenuation system are carried out for regimes corresponding to takeoff and cutback including the presence of coflow. The spectral characteristics and noise directivities in the far field are obtained for a wide range of azimuthal and polar angles. The results of these measurements are compared with two basic configurations: (i) one round nozzle with the same pressure and thrust as the rectangular nozzle; (ii) two identical round nozzles with the same pressure and total thrust as the rectangular nozzle. For equivalent jets corresponding to these two basic configurations, the noise in the far field is determined on the basis of the TsAGI semi-empirical method for calculating jet noise. The comparison with experimental data for the rectangular nozzle showed that there are ranges of observation angles and frequencies where noise reduction is obtained due to the use of the rectangular nozzle as compared to the equivalent round jets, and ranges where the rectangular nozzle is noisier. The recalculation of the spectra to the full scales and the assesment of SST noise in the EPNL metric show that the use of this rectangular nozzle can lead to the net effect of community noise reduction as compared to the round nozzles.