大涵道比涡扇发动机喷流降噪实验

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

对大涵道比分开排气喷管的缩比模型进行了吹风实验,模拟了双涵道喷流在加热条件下的远场噪声特性,分析了4种不同几何参数的锯齿构型对喷流噪声的影响。结果表明:喷流噪声以大尺度涡产生的低频噪声为主导,主要贡献方向为下游150°附近;锯齿喷管可以有效抑制低频部分及下游方向的噪声,最高可降低峰值声压级(SPL)约6 dB;锯齿的切入程度可以显著的影响降噪量,4种锯齿构型中切入程度高的外涵锯齿构型降噪效果最优,总声压级(OASPL)最高可降低3 dB;内涵锯齿构型的降噪效果比外涵锯齿低,总声压级最高降噪量在1 dB以内;内外涵锯齿构型可以在外涵锯齿的基础上进一步抑制低频噪声,下游方向总声压级最高降噪量为1.7 dB。

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.