Test of high-bypass-ratio turbofan engine jet noise reduction

A scale model test of high-bypass-ratio separated exhaust nozzle was conducted on the jet noise test facility for simulating a dual-stream hot flow to provide far-field noise characteristic of the turbofan engine. A baseline axisymmetric nozzle and four chevron nozzle were tested and analyzed to provide insight into some basic mechanisms and trends of this technology. Spectral and directivity results showed that high-bypass-ratio jet noise was mainly dominated by low frequency component generated by large scale turbulence, leading to the maximum directivity in 150 degree. Chevron nozzle was most effective at lower frequencies and at aft directivity angles, and the nozzle was shown to produce peak sound pressure level (SPL) reduction up to 6 dB. Penetration of chevron can significantly affect the noise reduction. Bypass chevron configuration with high penetration provided the best noise reduction among four chevron configurations, and the maximum over-all sound pressure level (OASPL) attenuation was 3 dB. Core chevron configuration reduction was less than bypass chevron configuration, in which the maximum OASPL attenuation was less than 1 dB. The combination of core and bypass chevron can lower SPLs compared with bypass chevron, and the maximum OASPL reduction was 17 dB.