The spectral broadening of sound by turbulent shear layers. Part 1. The transmission of sound through turbulent shear layers
The spectral broadening of sound by turbulent shear layers. Part 1. The transmission of sound through turbulent shear layers
复制标题
湍流剪切层导致声音频谱展宽。
DOI：
10.1017/s0022112078002827
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发表时间：
1978
影响因子：
3.7
通讯作者：
L. Campos
中科院分区：
文献类型：
--
作者：
L. Campos
从信号在传播过程中失真的数学理论出发，回顾了声音在湍流剪切层中的传播，并以此为基础，在第二部分中分析了与飞机噪声研究有关的实验结果所显示的频谱展宽。对于两种介质之间的不规则非定常界面的散射，利用相移和能量守恒定律、波数守恒定律和振幅守恒定律，得到了高频声在剪切层中被小尺度湍流绕射的反射系数和传输系数。这些结果可以用来构造从喷流内部的源穿过湍流剪切层的声场；在通过两个平行剪切层的情况下，即屏蔽噪声源的有限宽度的喷流，考虑了多个内反射。统计地描述了当能量被湍流绕射时透射波的衰减过程，以及折射波相关分量之间的干扰的部分补偿过程；参考情况是单色点源，当放置在剪切层系统之后时，其能量在方向上重新分配并在一定的频率范围内传播。所得到的能流表达式包括Howe(1975)和阻抗(1976)层的结果作为特例，湍流的影响与Schmidt&Tilmann(1970)和Ho&Kovasznay(1976a，b)的实验结果是一致的。
The transmission of sound through a turbulent shear layer is reviewed both with respect to the mathematical theory of the distortion of signals during propagation and also as the basis of the analysis in part 2 of the spectral broadening evinced by experimental results relevant to the study of aircraft noise. The reflexion and transmission coefficients, which involve both amplitude and phase changes, are obtained for scattering by an irregular and unsteady interface convected between two media; diffraction of high frequency sound by small-scale turbulence in a shear layer is accounted for by means of a phase shift and conservation laws for energy, wavenumber and amplitude. These results may be used to construct the sound field transmitted through a turbulent shear layer from a source in the interior of a jet; multiple internal reflexions are accounted for in the case of transmission through two parallel shear layers, i.e. a jet of finite width shielding a noise source. A statistical description is given of the process of attenuation of the transmitted wave as energy is diffracted by the turbulence, and of the partial compensation by interference between correlated components of the refracted wave; the reference case is a monochromatic point source, which, when placed behind a system of shear layers, has its energy redistributed directionally and spread over a range of frequencies. The expressions obtained for the energy flux include as particular cases the results of Howe for the plane (1975) and impedance (1976) layers, the effects of turbulence being shown to be consistent with the experiments of Schmidt & Tilmann (1970) and Ho & Kovasznay (1976a, b).