Investigation of aeroacoustic noise generation by simultaneous particle image velocimetry and microphone measurements
Investigation of aeroacoustic noise generation by simultaneous particle image velocimetry and microphone measurements
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DOI：
10.1007/s00348-008-0528-y
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发表时间：
2008-06
影响因子：
2.4
通讯作者：
A. Henning;Kristian Kaepernick;K. Ehrenfried;L. Koop;A. Dillmann
中科院分区：
文献类型：
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作者：
A. Henning;Kristian Kaepernick;K. Ehrenfried;L. Koop;A. Dillmann
相关技术进行测试，这使得识别的流动结构，参与声音生成过程。首先，将该方法应用于圆柱绕流的诱导噪声问题。采用粒子图像测速技术（PIV）测量圆柱周围的速度场，同时用传声器记录辐射声。两种测量都以同步的方式进行，以便能够计算速度或涡度波动与声压之间的互相关。由此获得的系数矩阵提供关于流结构与声压之间的统计依赖性的时间和空间分辨信息。此外，适当的正交分解（POD）的速度场。然后计算主模态和声压之间的相关性，以确定哪些模态主要参与声音产生。最后，将所发展的方法应用于更有应用价值的前缘缝翼内流场问题。结果表明，在这种情况下，信噪比太低，不允许识别噪声相关的流动结构，与圆柱尾流的情况相反，其中5,000个PIV记录足以识别噪声产生过程中涉及的流动结构。在空间分布的互相关系数的最大值观察1.6直径的圆柱体的下游，其值随着进一步向下游移动而减小。在最大相关性的这个区域中，发生释放的涡流的快速加速。互相关系数随时间以正弦型振荡形式波动，最大值约为，并表现出相互之间相移为π/2的周期性行为。这些规律性的振荡可以用流场中的相干周期结构来解释。这些结构产生具有相同周期性的声场，其被感知为音调。因此，速度波动和声压之间的相关性显示出与输入信号的振荡相同的振荡。可以观察到不相关噪声的滤波;这是由互相关计算期间的平均过程引起的。与POD的本征模的相关性给出相关系数，其不大于与局部近场量的相关性。
A correlation technique is tested, which enables the identification of flow structures that are involved in sound generation processes. At first, the method is applied to the problem of induced noise from flow over a cylinder. The velocity field around a circular cylinder is measured by particle image velocimetry (PIV), while the radiated sound is recorded with a microphone. Both measurements are conducted in a synchronized manner so as to enable the calculation of the cross-correlation between velocity or vorticity fluctuations and the acoustic pressure. The therewith obtained coefficient matrix provides time- and space-resolved information about the statistical dependency between flow structures and the acoustic pressure. Furthermore, a proper orthogonal decomposition (POD) is applied to the velocity field. Then the correlation between dominating modes and the acoustic pressure is computed to identify which modes are mainly involved in the sound generation. Finally, the developed method is applied to the more applied problem of the flow-field inside a leading-edge slat-cove. The results show that, in this case, the signal-to-noise ratio is too low to allow an identification of noise-relevant flow structures, as opposed to the case of the cylinder wake flow, where 5,000 PIV recordings were sufficient to identify the flow structures, which are involved in the noise-generation process. A maximum in spatial distribution of the cross-correlation coefficient is observed 1.6 diameters downstream of the cylinder; its value decreases as one moves further downstream. In this area of maximal correlation, a rapid acceleration of the released vortices takes place. The cross-correlation coefficient fluctuates over time in a sine-type oscillation with maximum values of aboutandshow a periodic behavior with a phase shift ofπ/2 with respect to each other. These regular oscillations can be explained by coherent periodic structures in the flow-field. These structures generate a sound field with the same periodicity, which is perceived as tone. Hence, the correlation between the velocity fluctuations and the acoustic pressure show oscillations identical to those of the input signals. A filtering of uncorrelated noise can be observed; this being caused by the averaging process during the cross-correlation calculation. The correlation with the eigenmodes of a POD gives correlation coefficients, which are no larger than the correlation with a local near-field quantity.