Correlations of jet noise azimuthal components and their role in source identification
Correlations of jet noise azimuthal components and their role in source identification
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喷射噪声方位分量的相关性及其在源识别中的作用
DOI：
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发表时间：
2010
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通讯作者：
I. Belyaev
中科院分区：
文献类型：
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作者：
V. Kopiev;S. Chernyshev;G. Faranosov;M. Zaitsev;I. Belyaev
在本文中，我们使用方位角分解技术（ADT）研究亚音速冷喷射噪声。报告了喷射噪声方位角分量相关性的测量结果。结果表明，音激励射流的相关性与非激励射流的相关性有很大不同；例如，对于与射流轴接近 90° 的观察角，获得了音调激发射流噪声方位角分量的出人意料的高相关值。这种相关性使其对于喷气噪声机制识别和源定位非常有前景。提出了一种基于四极源分布的分析模型来描述未激发射流噪声方位分量的相关性，并通过实验验证了其适用性。目前，湍流亚音速冷射流的噪声产生过程被认为与不同的机制有关：细尺度湍流（参考文献1和2）、大尺度涡结构的本征振荡（参考文献3）、不稳定波（参考文献4和5）等。在射流噪声产生过程中识别这些机制并评估它们对总噪声的贡献是一项重要的任务。然而，仅基于远场总噪声方向性的测量来实现这一点是困难的。远场噪声的方位分解使我们能够获得更详细的声源特征；先前对方位角分量建模的研究（参考文献3和6）表明，如果将大尺度涡结构（涡环）和细尺度湍流（建模为动点四极）作为声源，则可以解释观察到的冷亚音速射流噪声的实验数据，涡环对总噪声的贡献约为40%。已经观察到建模和实验曲线的良好崩溃，这表明这是模拟湍流冷亚音速喷气噪声的合理框架。为了进一步验证该模型并获得对声源结构的新见解，分析已扩展到包括方位角分量的相关特征。在参考文献中。 7 报道了非激励冷亚音速射流方位角谐波相关性测量的第一个结果（即在两个不同点对相同方位角模式同时测量之间的相关性），该结果通过实验验证了不同模式之间不存在相关性，这是从理论考虑中应该预期的（方位角分量是正交的）。 A 音调激发射流的互相关曲线具有特征性，尽管其形状通常与非激发射流曲线相似。这些曲线表明，大尺度结构声辐射集中在与射流成直角的区域，因为在该区域中，音激励射流的互相关曲线明显高于未激励射流的曲线。从一般观点来看，曲线的这种特性有点出乎意料，即射流中的大尺度结构在下游方向辐射，而在与射流方向成直角的方向上辐射的是所谓的细尺度湍流。在参考文献中。在图7中，已经获得了方位角分量的空间相关性，但没有尝试提出理论模型来解释观察到的空间相关性曲线。目前的工作中就做出了这样的尝试。声源被建模为移动点四极子的分布。将建模结果与速度为120 m/s的未激励冷射流远声场互相关函数测量结果进行了比较。对两个频带600中的零次谐波a0进行比较。实验装置
In this paper, we study the subsonic cold jet noise using the azimuthal decomposition technique (ADT). The results of measurement of correlations for jet noise azimuthal components are reported. It is shown that the correlations for tone-excited jet strongly differ from those for unexcited jet; for example, an unexpectedly high value of correlation for tone-excited jet noise azimuthal components has been obtained for observation angles close to 90o to the jet axis. This behavior of the correlation renders it quite promising for the jet noise mechanism identification and source localization. An analytical model based on qudrupole source distribution is proposed for description of the correlations for unexited jet noise azimuthal components and its applicability is validated experimentally. I. Introduction t present the process of noise generation by turbulent subsonic cold jets is thought to be related with different mechanisms: fine-scale turbulence (Refs. 1 and 2), eigen-oscillations of large-scale vortex structures (Ref. 3), instability waves (Refs. 4 and 5) etc. Identification of these mechanisms in the process of jet noise generation and assessment of their contribution to the total noise is an important task. To achieve this on the basis of the measurements of only far-field total noise directivity is difficult, however. The azimuthal decomposition of the far field noise allows us to obtain more detailed characteristics of the sound sources; the previous studies (Refs. 3 and 6) on modeling the azimuthal components show that the observed experimental data for cold subsonic jet noise can be explained if both large-scale vortex structures (vortex rings) and fine-scale turbulence (modeled as moving point quadrupoles) are accounted for as sound sources, the vortex rings’ contribution to the total noise being about 40%. An excellent collapse of the modeling and experimental curves has been observed, which evinces that this is a plausible framework to model turbulent cold subsonic jet noise. To further validate this model and get new insights into the structure of the sound sources, the analysis has been expanded to include correlation characteristics of the azimuthal components. In Ref. 7 the first results of correlation measurements of azimuthal harmonics for unexcited cold subsonic jets (i.e. the correlation between the simultaneous measurements for the same azimuthal mode at two different points) have been reported that experimentally verify the absence of correlation between different modes, which is what should be expected from the theoretical considerations (azimuthal components are orthogonal). A The cross-correlation curve for tone excited jet has characteristic peculiarities, albeit it is generally similar in shape to the unexcited jet curve. These curves demonstrate that the large-scale structure sound radiation is concentrated in the region at the right angle to the jet, because in this region the cross-correlation curve for the tone excited jet is significantly higher than the curve for the unexcited jet. This property of the curve is somewhat unexpected from the general view that large-scale structures in jet radiate in the downstream direction, whereas at the right angle to the jet direction it is so-called fine scale turbulence that radiates. In Ref. 7 the spatial correlations of the azimuthal components have been obtained, but no attempt has been made to propose a theoretical model to explain the observed spatial correlation curves. Such an attempt is made in the present work. The sound sources are modeled as a distribution of moving point quadrupoles. The results of modeling are compared with the results of measurements of cross-correlation function for the far sound field of unexcited cold jet with velocity 120 m/s. The comparison is performed for the zeroth harmonics a0 in two frequency bands 600. II. Experimental Setup