Far-Field Acoustic Investigation into Chevron Nozzle Mechanisms and Trends
Far-Field Acoustic Investigation into Chevron Nozzle Mechanisms and Trends
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DOI：
10.2514/1.6150
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发表时间：
2005
期刊：
影响因子：
2.5
通讯作者：
B. Callender;E. Gutmark;S. Martens
中科院分区：
文献类型：
--
作者：
B. Callender;E. Gutmark;S. Martens
雪佛龙喷嘴目前是降低中高涵道比涡轮风扇发动机喷气排气噪声的最可行方法之一。测试在辛辛那提大学喷嘴声学测试设施中进行，模拟单独的流动排气系统，以深入了解这项新兴技术的一些基本机制和趋势。在本研究中，在多种操作条件（包括双流和单流）下测试了基线内喷嘴和三个 V 形喷嘴。本研究选择了具有不同数量的波瓣和穿透程度的 V 形形状，以深入了解这些几何参数对噪声水平的影响。加热同轴流测试的频谱和方向性结果表明，V 形喷嘴在较低频率和后方向角时最有效。据记录，整体声压级 (SPL) 降低了 3 至 6 dB。感知噪声水平方向性的计算也显示在后角处降低了 4-6 dB。数据还表明了 V 形几何参数的清晰且一致的趋势。具体来说，V 形穿透被确定为控制低频降低和高频 SPL 增加之间权衡的主要因素。尽管在固定穿透力下观察到不同 V 形波瓣数的细微差异，但效果似乎不如穿透力显着。最后，数据表明 V 形效益明显依赖于内部流和外部流之间的速度差。
Chevron nozzles currently offer one of the most feasible methods of reducing jet exhaust noise in medium to high-bypass turbofan engines. Tests were conducted in the University of Cincinnati Nozzle Acoustic Test Facility, simulating a separate flow exhaust system to provide insight into some of the basic mechanisms and trends of this emerging technology. For this study, a baseline inner nozzle and three chevron nozzles were tested over a wide range of operating conditions, including dual and single flow. Chevrons with varying numbers of lobes and levels of penetration were selected for this study to provide insight into the impact of these geometric parameters on the noise level. Spectral and directivity results from heated, coaxial flow tests showed that the chevron nozzles are most effective at lower frequencies and at aft directivity angles. Reductions in overall sound pressure level (SPL) ranging from 3 to 6 dB were documented. Calculations of perceived noise level directivity also showed 4-6 dB reduction at aft angles. The data also illustrated clear and consistent trends with respect to the chevron geometric parameters. Specifically, the chevron penetration was determined to be a primary factor in controlling the tradeoff between low-frequency reduction and high-frequency SPL increases. Although slight differences were observed with varying chevron lobe numbers at a fixed penetration, it appears that the effect is less significant than the penetration. Finally, the data indicated clear dependence of the chevron benefit on the velocity difference between the inner and outer streams.