Jet Noise Reduction Using Microjet Configurations Experimental Characterization In CEPRA19 Anechoic Wind Tunnel

Research of jet noise reduction by adaptive microjets injection has been conducted under a collaboration research project between JAXA, IHI in Japan and Onera, Snecma in France. At first, IHI was responsible for microjets noise reduction on a Low Bypass Ratio (BPR) engine nozzle dedicated to a high speeds aircraft, and Onera was in charge of development and operation of upstream simulator used for generating microjets flow in the facility. In parallel, JAXA and Onera have been developing Large Eddy Simulation (LES) tools to understand the microjet noise reduction mechanisms. In this paper, we intend to focus on jet noise measurements around a large scale low BPR engine nozzle attached to the microjets simulator. The new microjets simulator has the capability to supply a maximum of 32 cold flow microjets into the bypass flow. The low BPR model with 125 mm nozzle diameter was designed according to primary flow (900K hot gas) and secondary flow (380K compressed air). Moreover, three types of microjet rings were tested; they could easily be changed by removing the nozzle exit, in addition, low pressure loss until blowing. As a result, the noise benefit of microjet is up to approximately 0.9EPNLdB even in flight condition. On the other hand, the turbulence kinetic energy and Reynolds stress that is associated with jet noise production was observed in the time-averaged LES result. Three typical features of low BPR nozzle were confirmed through cross section view. Microjet can deform main jet shear layer when 1% blowing, however the shock wave of the main jet was not terminated by the microjet.