Extracting Coherent Structures to Explore the Minimum Jet Noise
Extracting Coherent Structures to Explore the Minimum Jet Noise
复制标题
提取相干结构以探索最小射流噪声
DOI：
10.1142/9789814635165_0035
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
P. Jordan
中科院分区：
文献类型：
--
作者：
Zhidong Fu;A. Agarwal;A. Cavalieri;P. Jordan
本文研究了在给定射流出口速度和喷嘴尺寸的情况下，圆形湍流冷射流（马赫数 0.88）辐射到远场的声音下限。通过在方位角应用离散小波变换（DWT）和傅立叶变换，射流被分解为波包（WP）、相干涡流（CE）和非相干结构（IS）。在流体动力近场的时间平均分量不变的情况下，使用小波滤除 WP。结果表明，剩余的 IS（根据定义具有高斯 PDF）是去相关的。使用相同的方法，声学远场在低方位角模式下被过滤，与原始射流相比，不同轴向角度下的整体远场声音降低了 9-15dB。声谱显示高频分量占主导地位并且不受滤波过程的影响。去除IS后，近场和远场的轴对称模态之间的相关性值明显高于所报告的轴对称模态的流声相关性的值。建议在给定所提出的约束条件下，过滤所有模态后的声音降低是实践中可以实现的最佳效果。
This paper examines the lower bound of the sound that a circular turbulent cold jet (Mach number 0.88) radiates to the far field, for the given jet exit velocity and nozzle size. By applying discrete wavelet transform (DWT) and Fourier transform in azimuth, the jet flow is decomposed into wave packets (WP), coherent eddies (CE), and incoherent structures (IS). With the time-averaged component of the hydrodynamic near field unchanged, WP are filtered out using wavelets. It is shown that the remaining IS, which has a Gaussian PDF by definition, is de-correlated. Using the same approach, the acoustic far field is filtered in the low azimuthal modes, leading to 9-15dB lower overall far-field sound compared with the original jet at different axial angles. Sound spectra show that the high-frequency component dominates and remains unaffected by the filtering process. After IS are removed, the values of the correlations between the axisymmetric modes of the near and far field are significantly higher than those reported for flow-acoustic correlations of the axisymmetric mode. It is suggested that the sound reduction after all modes are filtered is the best that can be achieved in practice, given the proposed constraints.