REDUCTION OF EJECTOR NOISE WITH MULTIHOLE NOZZLE

In order to reduce the noise, an ejector with multihole nozzle is proposed as the primary nozzle, and its design method is presented. For comparison of the aerodynamic performance and the noise characteristics with those of conventional one in subsonic and supersonic ejector systems, the sound power levels and the primary and secondary mass flow rates of the ejectors were measured, and the static thrusts of the ejectors were estimated, based on the measured mass flow rates. The shroud length of the ejector system tested was altered in the experiments so as to study the effect of this parameter on noise and thrust. The exper imental results show that the multihole nozzle ejector system not only reduces noise considerably but also gains better aerodynamic performance due to a shorter shroud. The shorter the shroud, the more noise reduction and greater the static thrust increment can be achieved. For subsonic ejector, the noise reduction is about 14dB and the static thrust increment is about 30% when ratio of shroud length is 7.6. For supersonic ejector, those are about 22dB and 35% respectively when the shroud length ratio is 9.6.