This paper describes an experimental study on the acoustic performance when mixer nozzles were applied to the core of a subscale turbofan engine. The primary concern of the mixer nozzle is how to satisfy both less jet mixing noise emission and minimum impact on engine performance parameters such as thrust and fuel consumption. A notched nozzle, a nozzle with tiny dents on the trailing edge, initiates small disturbances in the shear layer, weakens the shear stress, and suppresses jet noise. The Japan Aerospace Exploration Agency (JAXA) and IHI Corporation have studied notched nozzles and found that finer and more notches are preferable for both acoustic and aerodynamic performance.
As a next step, it is necessary to maintain the tradeoff between noise suppression and impact on engine performance. To evaluate both the acoustic and aerodynamic performance with the notched nozzle, a subscale turbofan engine, DGEN380, was adopted as a demonstration engine. Experiments with this engine were conducted both in a test cell and in an open test site. The notched nozzle, together with a baseline conical nozzle and a referential serrated nozzle, i.e., a chevron nozzle, was applied to the core exhaust of the engine.
The experiment in the test cell clarified that the notched nozzle possibly provides better thrust specific fuel consumption than the referential chevron nozzle. The acoustic measurement in the open environment confirmed that the notched nozzle has the noise suppression characteristics expected from previous test results. The perceived noise levels are attenuated by 1.5 dB, which is the same as or better than the referential mixer nozzle.