Large-scale structure evolution and sound emission in high-speed jets: real-time visualization with simultaneous acoustic measurements
Large-scale structure evolution and sound emission in high-speed jets: real-time visualization with simultaneous acoustic measurements
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DOI：
10.1017/s002211200500666x
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发表时间：
2005-12-10
影响因子：
3.7
通讯作者：
Samimy, M
中科院分区：
文献类型：
--
作者：
Hileman, JI;Thurow, BS;Samimy, M
本研究提出了一套独特而详尽的实验，将噪声的产生与理想膨胀、1.28马赫、高雷诺数（1.03 x 10(6)）射流中大规模湍流结构的演变联系起来。结果表明高速低雷诺数射流和高速高雷诺数射流的噪声产生过程有许多相似之处。与以往实验和计算中观察到的低雷诺数射流噪声产生区域的快速变化类似，在噪声发射前，一系列鲁棒流动特征在大约一个对流时间尺度上形成，然后在噪声发射估计时刻前不久迅速解体。与解体相一致的是，一个正的图像强度波动在喷流中心线形成，在一个区域，直接超过潜在核心的末端。这表明混合流体已经到达喷流核心。这些结果与剪切层内大型结构的形成一致，这些结构将环境空气带入射流，它们最终的相互作用和解体明显导致噪声的产生。这些结果与缺乏显著声发射的长时间射流的演变有很大不同。在这项工作中提出的观察是通过使用成熟的技术，以一种非常规的方式汇集在一起。采用一种新颖的传声器阵列/波束形成算法对大振幅声源进行时间和三维空间估计，同时在两个正交平面上同时显示混合层的噪声产生区域（其中一个平面进行了时间分辨）。根据流动成像时在流动区域内是否产生声波，对流动图像进行有条件的采样，并编译一系列图像，这些图像大致锁定在声发射时刻。另一组图像是基于在几个对流时间尺度上没有声波到达麦克风阵列而收集的。然后利用适当的正交分解（POD）为流动图像创建一个基，并利用该基重建射流的演变过程。
This investigation presents a unique and elaborate set of experiments relating the generation of noise to the evolution of large-scale turbulence structures within an ideally expanded, Mach 1.28, high-Reynolds-number (1.03 x 10(6)) jet. The results appear to indicate many similarities between the noise generation processes of highspeed low-Reynolds-number and high-speed high-Reynolds-number jets. Similar to the rapid changes observed in the region of noise generation in low-Reynolds-number jets in previous experimental and computational work, a series of robust flow features formed approximately one convective time scale before noise emission and then rapidly disintegrated shortly before the estimated moment of noise emission. Coincident with the disintegration, a positive image intensity fluctuation formed at the Jet centreline in a region that is immediately past the end of the potential core. This indicates mixed fluid had reached the jet core. These results are consistent with the formation of large-scale structures within the shear layer, which entrain ambient air into the jet, and their eventual interaction and disintegration apparently result in noise generation. These results are quite different from the evolution of the jet during prolonged periods that lacked significant sound emission. The observations presented in this work were made through the use of well-established techniques that were brought together in an unconventional fashion. The sources of large-amplitude sound waves were estimated in time and three-dimensional space using a novel microphone array/beamforming algorithm while the noise-generation region of the mixing layer was simultaneously visualized on two orthogonal planes (one of which was temporally resolved). The flow images were conditionally sampled based on whether or not a sound wave was created within the region of the flow while it was being imaged and a series of images was compiled that was roughly phase-locked onto the moment of sound emission. Another set of images was gathered based on a lack of sound waves reaching the microphone array over several convective time scales. Proper orthogonal decomposition (POD) was then used to create a basis for the flow images and this basis was used to reconstruct the evolution of the jet.