Spectral broadening of acoustic waves by convected vortices
Spectral broadening of acoustic waves by convected vortices
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DOI：
10.1017/jfm.2018.94
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发表时间：
2018-02
影响因子：
3.7
通讯作者：
V. Clair;G. Gabard
中科院分区：
文献类型：
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作者：
V. Clair;G. Gabard
在两个维度上研究了运动涡旋对声波的散射，以进一步了解湍流区域引起的光谱展宽的物理机制。当通过湍流传播时，单色声波将在一定的频率范围内散射，导致在音调的两侧具有宽带旁瓣的典型频谱。这种光谱增宽，也称为“干草堆”，对于喷气式排气的噪声辐射和开放式喷气式风洞中的声学测量是重要的。本文建立了一个考虑涡旋对流影响的涡旋散射平面波的半解析模型。这使我们能够进行详细的参数研究的属性和散射场的演变。线性化欧拉方程的时域数值模型也被用来考虑更一般的声场，如均匀流中的点源辐射。频谱展宽源于声音的空间散射的组合，由于通过涡旋传播的波的折射，和两个多普勒频移诱导的涡旋相对于源的运动和观察者相对于涡旋。光谱出现边带的事实可以直接用散射场的方向性来解释，散射场是由从涡旋辐射的几个光束组成的。与本文所考虑的参数的声学谱的演变进行了比较，在以前的实验工作中观察到的趋势声散射射流剪切层。
The scattering of acoustic waves by a moving vortex is studied in two dimensions to bring further insight into the physical mechanisms responsible for the spectral broadening caused by a region of turbulence. When propagating through turbulence, a monochromatic sound wave will be scattered over a range of frequencies, resulting in typical spectra with broadband sidelobes on either side of the tone. This spectral broadening, also called ‘haystacking’, is of importance for noise radiation from jet exhausts and for acoustic measurements in open-jet wind tunnels. A semianalytical model is formulated for a plane wave scattered by a vortex, including the influence of the convection of the vortex. This allows us to perform a detailed parametric study of the properties and evolution of the scattered field. A time-domain numerical model for the linearised Euler equations is also used to consider more general sound fields, such as that radiated by a point source in a uniform flow. The spectral broadening stems from the combination of the spatial scattering of sound due to the refraction of waves propagating through the vortex, and two Doppler shifts induced by the motion of the vortex relative to the source and of the observer relative to the vortex. The fact that the spectrum exhibits sidebands is directly explained by the directivity of the scattered field which is composed of several beams radiating from the vortex. The evolution of the acoustic spectra with the parameters considered in this paper is compared with the trends observed in previous experimental work on acoustic scattering by a jet shear layer.