冠状喷口抑制涡扇发动机喷流噪声试验和数值研究

 以揭示发动机喷流噪声声场分布和冠状喷口抑制喷流噪声为目的,对涡扇发动机排气噪声声场和喷流流场进行了试验和数值计算,对比分析不同结构的冠状锯齿对喷流噪声的综合抑制效果。结果表明:采用大涡模拟(LES)、FW-H (Ffowcs Williams-Hawkings)声学模型和傅里叶变换的方法,可以预测出喷流噪声的空间分布和声压级值;冠状锯齿产生的阵列流向涡是强化流体间混合、降低喷流速度峰值、抑制喷流噪声的根本所在;在本文研究参数范围内,冠状锯齿结构不仅将排气喷流噪声由原型排气系统的159.6 dB降低到154.3 dB,而且冠状锯齿给喷管带来的损失控制在1.7%以内。锯齿冠状结构对分开排气式大涵道比涡扇排气系统喷流噪声有抑制作用。

Experimental and Numerical Research on Jet Noise Suppression with Chevron Nozzle for Turbofan Engines

In order to reveal the space distribution of jet noise and suppress it, the unsteady flow field and the jet noise distribution of overall sound pressure level are obtained for various geometric structures of chevron nozzles based on large eddy simulation (LES) and FW-H (Ffowcs Williams-Hawkings) acoustics equation for the separated exhaust systems of turbofan engines. The results show that the stream vortices produced by the chevron is the key for the suppression of the jet noise. An enhanced mixture between the bypass flow and the environment, or between the bypass flow and the core flow, decreases the jet peak velocity. In the range of the geometry parameters of chevron nozzles mentioned in this paper, an exhaust nozzle with chevrons can suppress the jet noise to 154.3 dB as compared with the 159.6 dB of the exhaust system without a chevron nozzle. Meantime, the aerodynamic loss caused by it is only 1.7%. The study thus demonstrates that the chevron nozzle has an active noise suppression function for the separated exhaust system of a turbofan engine.