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首页> 外文期刊>Journal of Fluid Mechanics >Large-scale structure evolution and sound emission in high-speed jets: real-time visualization with simultaneous acoustic measurements
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Large-scale structure evolution and sound emission in high-speed jets: real-time visualization with simultaneous acoustic measurements

机译：高速喷气机中的大型结构演变和声音发射：实时可视化，同时进行声学测量

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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.
机译：这项研究提出了一套独特而精心设计的实验，这些实验将噪声的产生与理想扩展的马赫数1.28，高雷诺数（1.03 x 10（6））射流内的大规模湍流结构的演化联系起来。结果似乎表明，高速低雷诺数喷气机和高速高雷诺数喷气机的噪声产生过程之间有许多相似之处。与先前的实验和计算工作中在低雷诺数喷气机的噪声产生区域中观察到的快速变化类似，一系列稳健的流动特征在噪声释放之前形成了大约一个对流时间尺度，然后在估计时刻前不久迅速分解的噪音。伴随着崩解，在正好超过电位核心末端的区域中，Jet中心线处形成了正的图像强度波动。这表明混合流体已经到达射流芯。这些结果与在剪切层内形成大型结构相一致，该结构将周围的空气夹带到射流中，并且它们最终的相互作用和分解显然导致产生噪声。这些结果与缺乏明显声音发射的长时间喷流的演变完全不同。这项工作中提出的意见是通过使用公认的技术以非常规的方式结合在一起进行的。使用新颖的麦克风阵列/波束形成算法，在时间和三维空间中估计了大振幅声波的来源，同时在两个正交平面上同时可视化了混合层的噪声产生区域（其中一个在时间上得到了解析） 。根据在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采样，然后编译一系列图像，这些图像大致锁相在发出声音的时刻。基于在几个对流时间尺度上缺少到达麦克风阵列的声波，收集了另一组图像。然后使用适当的正交分解（POD）为流动图像创建基础，并使用该基础重建射流的演化。

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