Investigation of noise sources in high-speed jets via correlation measurements
Investigation of noise sources in high-speed jets via correlation measurements
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DOI：
10.1017/s0022112005005148
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发表时间：
2005-08-25
影响因子：
3.7
通讯作者：
Elam, KA
中科院分区：
文献类型：
--
作者：
Panda, J;Seasholtz, RG;Elam, KA
为了定位高速射流中的噪声源，将远场声压波动p'与密度rho、轴向速度u、径向速度v、rho uu和rho vv在射流羽流中不同位置测量的波动进行关联。详细的调查是在完全膨胀的、0.95马赫、1.4马赫和1.8马赫的未加热羽流中进行的。采用一种基于分子瑞利散射的非侵入式点测量技术同时测量了速度和密度波动。该技术使用连续波窄线宽激光器、法布里-珀罗干涉仪和光子计数电子设备。该干涉仪收集了空气分子在窄光束上1.06 mm长区域散射的激光，并对其进行了光谱分辨。结果表明，羽流内部空气密度的波动谱与轴向速度谱基本相似，而径向速度谱则略有不同。在相关性研究中，麦克风极角与射流轴的夹角从30°到90°不等。在最浅的30度角处，声压波动p与湍流波动的相关性最高。当极角增加到60度时，相关性急剧下降，超过60度后，所有数据大多低于实验噪声底限。在所有湍流波动中，与90度麦克风信号的相关性低于实验噪声底，而来自浅30度麦克风的相关性较弱。通过将激光探针移动到射流中的不同位置，发现最强的噪声源位于势核末端的下游，并向外延伸了许多直径。沿唇缘剪切层湍流波动的相关测量显示了马赫数依赖性：在超音速射流中测量到显著值，而在亚音速射流中相关性低于噪声底。各种附加分析表明，来自大型相干结构的波动主要有助于测量到的相关性，而来自小型结构的波动则低于噪声底。
To locate noise sources in high-speed jets, the far-field sound pressure fluctuations p' were correlated with each of density rho, axial velocity u, radial velocity v, rho uu and rho vv fluctuations measured from various points in jet plumes. Detailed surveys were conducted in fully expanded, unheated plumes of Mach 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed non-intrusive point measurement technique based on molecular Rayleigh scattering. The technique uses a continuous-wave narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. Laser light scattered by air molecules from a 1.06 mm long region on the narrow beam was collected and spectrally resolved by the interferometer. It was observed that the fluctuation spectra for air density inside the plume were in general similar to those of axial velocity spectra, while the radial velocity spectra were somewhat different. For the correlation study, microphone polar angles were varied from 30 degrees to 90 degrees to the jet axis. The sound pressure fluctuations p, at the shallowest 30 degrees angle provided the highest correlation with turbulent fluctuations. The correlations sharply decreased as the polar angle was increased to 60 degrees, beyond which all data mostly fell below the experimental noise floor. Among all turbulent fluctuations and correlations with the 90 degrees microphone signal fell below the experimental noise floor, while that from the shallow 30 degrees microphone showed weaker values. By moving the laser probe to various locations in the jet, it was found that the strongest noise source lay downstream of the end of the potential core and extended many diameters beyond. Correlation measurements from turbulent fluctuations along the lip shear layer showed a Mach-number dependency: significant values were measured in supersonic jets, while correlations fell below the noise floor for subsonic jets. Various additional analyses showed that fluctuations from large coherent structures mostly contributed to the measured correlation, while that from small-scale structures fell below the noise floor.