MODELLING OF THE NOISE SPECTRA OF AXIAL FLOW FANS IN A FREE FIELD
MODELLING OF THE NOISE SPECTRA OF AXIAL FLOW FANS IN A FREE FIELD
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DOI：
10.1006/jsvi.1996.0705
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发表时间：
1997-03
影响因子：
4.7
通讯作者：
Sean F. Wu;S. Su;H. Shah
中科院分区：
文献类型：
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作者：
Sean F. Wu;S. Su;H. Shah
本文提出了轴流风机在自由场中噪声谱的半经验预测公式。在推导该公式时所作的基本假设是，轴流风机在自由场中的声辐射主要是由于施加在风机叶片表面的脉动压力。这种脉动压力与作用在风扇叶片上的单位长度的升力相关，随后被在空间和时间上衰减的压力脉冲近似。因此，辐射声压被表示为这些压力脉冲的贡献的叠加，并且通过傅立叶级数展开获得线谱。为了模拟窄频带和宽带声谱，设计了一种类正态分布的形函数，以叶片通过频率及其谐波为中心，将频率划分为连续的频段。该形函数在每个频段的中心频率处的幅度是单位的，但按指数衰减。衰减率随能带数目的增加而减小。因此，在高频下，窄带合并形成宽带状光谱。将所测得的噪声谱与四种不同类型轴流风机在不同工况下的实测值进行了比较，得到了较好的一致性。
This paper presents a semi-empirical formula for predicting the noise spectra of axial flow fans in a free field. The basic assumption made in deriving this formula is that sound radiation from an axial flow fan in a free field is primarily due to the fluctuating pressure exerted on the fan blade surface. This fluctuating pressure is correlated to the lift force per unit length acting on the fan blade, and is subsequently approximated by pressure pulses that decay both in space and time. Accordingly, the radiated acoustic pressure is expressed in terms of superposition of contributions from these pressure pulses, and the line spectrum is obtained by taking a Fourier series expansion. To simulate the narrow and broad band sound spectra, a normal distribution-like shape function is designed which divides the frequency into consecutive bands centered at the blade passage frequency and its harmonics. The amplitude of this shape function at the center frequency of each band is unity but decays exponentially. The decay rate decreases with an increase in the number of bands. Thus, at high frequencies the narrow bands merge to form broad band-like spectra. The noise spectra thus obtained are compared with the measured ones from four different types of axial flow fans running under various conditions, and a favorable agreement in each case is obtained.