在低速湍流边界层中重新探讨相干结构

2019/12/02   下载量： 1 次

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采用LaVision的时间分辨体视层析粒子成像测速系统(TRTOMO-PIV)对低速湍流边界层中流场的相干结构进行了详细讨论和研究。

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Coherent structures are essential for the momentum exchange and turbulence production in wall-bounded turbulent flows. Diversified coherent structures have been observed in turbulent boundary layers, and hairpin-based vortices dominate most of the relevant literature. However, there is no consensus yet on the origin and forming mechanism of hairpin vortices. Herein, five corner stones pertaining to the framework of hairpin-based coherent structures are reviewed, and three different hairpin generation mechanisms are clarified. Next, the time-resolved tomographic particle image velocimetry (Tomo-PIV) is used in an early turbulent boundary layer (Reθ = 420) to investigate the origin of hairpin vortices. The timelines reveal a triangular bulge in the low-speed streak (LSS), and the initial roll-up occurs at two sides of it. Meanwhile, the material surfaces manifest as a three-dimensional (3D) wave structure in the LSS, which may support the model of a soliton-like coherent structure (SCS). Subsequently, the method of Lagrangian-averaged vorticity deviation is used to detect early vortices. We find that the 3D wave structure is flanked by two vortices, thus confirming the roll-up of timelines and demonstrating the advantage of the Lagrangian criteria in capturing structures in complex flows. These results suggest that various coherent structures may evolve from the
metamorphosis of 3D wave structures and their later interaction. Finally, the limitations
of traditional experimental and post-processing tools are discussed

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北京欧兰科技发展有限公司
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