Mechanisms of Jet Noise Generation: Classical Theories and Recent Developments
Mechanisms of Jet Noise Generation: Classical Theories and Recent Developments
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射流噪声产生机制：经典理论和最新进展
DOI：
10.1260/147547209787548949
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发表时间：
2009
影响因子：
1
通讯作者：
K. Viswanathan
中科院分区：
文献类型：
--
作者：
K. Viswanathan
莱特希尔的声学类比和它的几个变体已被用来解释，分析和解释测量数据。在本文中，经典理论的主要原则的有效性进行了检查。一个新的综合航空声学数据库为这项评估提供了便利。总声功率级并不完全遵循速度的八次方（Vj/a），但对射流温度的依赖性较弱。人们认为，对于加热的喷流，会出现额外的噪音源，其随速度的六次或四次变化;在90°处，频谱形状也会发生假设的变化，尽管与对流和流动/声学相互作用相关的影响在该角度可以忽略不计。新的数据表明，即使在3.2的非常高的滞止温度比下，总功率的速度指数也接近8。此外，频谱形状与射流马赫数和射流温度无关。Tanna的数据库为许多理论模型提供了基本原理和理由，对该数据库的仔细评估表明，该数据库不可靠，并且呈现出不正确的光谱趋势。经典理论的一个基本原则是移动源的概念，它建立在莱特希尔-弗福克斯威廉姆斯和利莱的形式主义基础上。这种想法立即导致频率的多普勒频移和辐射到后角的噪声的对流放大因子。新的数据库表明，没有实验证据表明这些移动源的约束效应。射流温度比（静态或停滞），除了射流速度Vj/a，是一个独立的控制参数。利用现有数据库，已开发出适用于所有角度的新比例定律。谱函数不存在可调常数的乘法因子，谱函数和速度指数依赖于射流温度比和辐射角。这一关系是当前公式与经典公式之间的主要区别。一个单一的指数崩溃的整个频谱从射流具有不同的Vj/a，但在固定的射流温度比。因此，没有实验证据证明喷气噪声的主要经典思想，包括多极和移动源，因为它们与新数据不一致。研究了喷流的细尺度和大尺度湍流的两个不同来源的概念。即使在低速度的噪声从大相干结构的重要性的实验证据。在较低和较大的后角上观察到的不同特征，（1）远场频谱形状，（2）峰值Strouhal数和OASPL的方向性，（3）速度指数的方向性，和（4）远场压力的极相关和方位相关，提供了强有力的证据来支持上述两种不同的喷流噪声源的观点。
Lighthill's acoustic analogy and several variants of it have been used to interpret, analyze and explain measured data. In this paper, the validity of the main tenets of the classical theories is examined. This assessment is facilitated by a new comprehensive aeroacoustic database. The overall sound power level does not exactly follow the eighth power of velocity (Vj/a), but has a weak dependence on jet temperature. It has been believed that an additional source of noise, with either sixth or fourth power variation with velocity, appears for heated jets; there is also a supposed change in spectral shape at 90°, even though effects associated with convection and flow/acoustic interaction are negligible at that angle. The new data indicate that the velocity exponent for overall power is close to eight even at a very high stagnation temperature ratio of 3.2. Moreover, the spectral shape is invariant with jet Mach number and jet temperature. A careful assessment of Tanna's database, which provided the rationale and justification for many of the theoretical models, reveals that this database is unreliable and exhibits incorrect spectral trends. A fundamental tenet of the classical theories, based on both the formalisms of Lighthill-Ffowcs Williams and Lilley, is the notion of moving sources. This idea immediately leads to a Doppler shift for frequency and a convective amplification factor for the noise radiated to the aft angles. It is demonstrated with the new database that there is no experimental evidence for these conjectured effects of moving sources. The jet temperature ratio (static or stagnation), in addition to jet velocity Vj/a, is an independent controlling parameter. New scaling laws that are valid for all angles have been developed with the current database. There are no multiplicative factors with adjustable constants for the spectrum functions; the spectrum function and the velocity exponent depend on the jet temperature ratio and the radiation angle. This relation represents the main difference between the current and the classical formulations. A single exponent collapses the entire spectrum from jets with different Vj/a, but at fixed jet temperature ratio. Therefore, there is no experimental evidence for the main classical ideas of jet noise, as consisting of multi-poles and moving sources, as they are inconsistent with the new data. The idea of two distinct sources that are related to the fine-scale and large-scale turbulence of the jet plume has been investigated. Experimental evidence for the importance of the noise from large coherent structures even at low velocities is offered. The observation at lower and large aft angles of distinct characteristics in, (1) the far field spectral shapes, (2) the directivities of the peak Strouhal number and the OASPL, (3) the directivity of the velocity exponent, and (4) the polar and azimuthal correlations of the farfield pressure, provides strong evidence to support the above view of two different sources of jet noise.