Rolls-Royce Turbomeca Adour MK151
羅爾斯-羅伊斯透博梅卡公司
阿杜爾”（Adour）Mk151發動機
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
奈皮爾公司
“蓋茲爾”發動機
Royce in 1961.
“蓋茲爾”渦輪軸發動機于1955年12月首次試車，當時的功率為1260軸馬力，后來，在生產型發動機上，功率增至1610軸馬力。“蓋茲爾”發動機用于布里斯托（Bristol）公司的“了望塔”（Belvedere）和韋斯
特蘭（Westland）公司的“威賽克斯”（Wessex）直升機。“蓋茲爾”發動機的生產于1961年由羅爾斯-羅伊斯公司接管。
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.
總的趨勢
有效感覺噪聲分貝
無噪聲抑制器的純噴氣發動機
有噪聲抑制器的純噴氣發動機
低涵道比噴氣發動機
高涵道比噴氣發動機
Noise suppression
圖19-1 不同類型發動機的噪聲水平比較
大渦流
（低頻噪聲）
小渦流
（高頻噪聲）
激波
混合區
排氣道
排氣流核心
頻率
混合噪聲
聲級
激波噪聲
總噪聲
Fig. 19-1 Comparative noise levels of various engine types.
19-2 排氣混合和激波結構
Fig. 19-2 Exhaust mixing and shock structure.
5.噴氣流噪聲是由于排出的燃氣與大氣猛烈地撞擊，因而產生紊流度極強的混合所造成的。它受由排氣流和大氣之間的相對速度引起的剪切作用的影響。在排氣口附近產生的小渦流引起高頻噪聲，但是，在排氣流后部大的渦流產生低頻噪聲。另外，當排氣流速度超過當地音速時，在排氣流核心部分形成形狀有規律的激波。這就產生一離散的(單一頻率)聲調，并將混合噪聲有選擇性地放大，如圖19-2所示。如果混合速度加快或噴氣流相對于大氣的速度減小，噪聲水平就會降低。這借助于改變噴氣流的形狀就可以辦到，如圖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
