Rolls-Royce Turbomeca Adour MK151
罗尔斯-罗伊斯透博梅卡公司
阿杜尔”（Adour）Mk151发动机
The Gazelle turbo-shaft engine first ran in December 1955 at 1260 shp, a figure later increased to 1610 shp on production engines. Gazelles were used to power Bristol Belvedere and Westland Wessex helicopters. Gazelle production was taken over by Rolls-
Napier Gazelle
奈皮尔公司
“盖兹尔”发动机
Royce in 1961.
“盖兹尔”涡轮轴发动机于1955年12月首次试车，当时的功率为1260轴马力，后来，在生产型发动机上，功率增至1610轴马力。“盖兹尔”发动机用于布里斯托（Bristol）公司的“了望塔”（Belvedere）和韦斯
特兰（Westland）公司的“威赛克斯”（Wessex）直升机。“盖兹尔”发动机的生产于1961年由罗尔斯-罗伊斯公司接管。
INTRODUCTION
1.
Airport regulations and aircraft noise certification requirements, all of which govern the maximum noise level aircraft are permitted to produce, have made jet engine noise suppression one of the most important fields of research.
2.
The unit that is commonly used to express noise annoyance is the Effective Perceived Noise deciBel (EPNdB). It takes into account the pitch as well as the sound pressure (deciBel) and makes allowance for the duration of an aircraft flyover. Fig. 19-1 compares the noise levels of various jet engine types.
3. Airframe self-generated noise is a factor in an aircraft's overall noise signature, but the principal noise source is the engine.
ENGINE NOISE
4. To understand the problem of engine noise suppression, it is necessary to have a working knowledge of the noise sources and their relative importance. The significant sources originate in the fan or compressor, the turbine and the exhaust jet or jets. These noise sources obey different laws and mechanisms of generation, but all increase, to a varying degree, with greater relative airflow velocity. Exhaust jet noise varies by a larger factor than the compressor or turbine noise, therefore a reduction in exhaust jet velocity has a stronger influence than an equivalent reduction in compressor and turbine blade speeds.
总的趋势
有效感觉噪声分贝
无噪声抑制器的纯喷气发动机
有噪声抑制器的纯喷气发动机
低涵道比喷气发动机
高涵道比喷气发动机
Noise suppression
图19-1 不同类型发动机的噪声水平比较
大涡流
（低频噪声）
小涡流
（高频噪声）
激波
混合区
排气道
排气流核心
频率
混合噪声
声级
激波噪声
总噪声
Fig. 19-1 Comparative noise levels of various engine types.
19-2 排气混合和激波结构
Fig. 19-2 Exhaust mixing and shock structure.
5.喷气流噪声是由于排出的燃气与大气猛烈地撞击，因而产生紊流度极强的混合所造成的。它受由排气流和大气之间的相对速度引起的剪切作用的影响。在排气口附近产生的小涡流引起高频噪声，但是，在排气流后部大的涡流产生低频噪声。另外，当排气流速度超过当地音速时，在排气流核心部分形成形状有规律的激波。这就产生一离散的(单一频率)声调，并将混合噪声有选择性地放大，如图19-2所示。如果混合速度加快或喷气流相对于大气的速度减小，噪声水平就会降低。这借助于改变喷气流的形状就可以办到，如图19-3所示。
5. Jet exhaust noise is caused by the violent and hence extremely turbulent mixing of the exhaust gases with the atmosphere and is influenced by the shearing action caused by the relative speed between the exhaust jet and the atmosphere. The small eddies created near the exhaust duct cause high frequency noise but downstream of the exhaust jet the larger eddies create low frequency noise. Additionally, when the exhaust jet velocity exceeds the local speed of sound, a regular shock pattern is formed within the exhaust jet core. This produces a discrete (single frequency) tone and selective ampli-fication of the mixing noise, as shown in fig. 19-2. A reduction in noise level occurs if the mixing rate is accelerated or if the velocity of the exhaust jet relative to the atmosphere is reduced. This can be achieved by changing the pattern of the exhaust jet as shown in fig. 19-3.
Noise suppression
6. Compressor and turbine noise results from the interaction of pressure fields and turbulent wakes from rotating blades and stationary vanes, and can be defined as two distinct types of noise; discrete tone (single frequency) and broadband (a wide range of frequencies). Discrete tones are produced by the regular passage of blade wakes over the stages downstream causing a series of tones and harmonics from each stage. The wake intensity is largely dependent upon the distance between the rows of blades and vanes. If the distance is short then there is an intense pressure field interaction which results in a strong tone being generated. With the high bypass engine, the low pressure compressor (fan) blade wakes passing over downstream vanes produce such tones, but of a lower intensity due to lower velocities and larger blade/vane separations. Broadband noise is
