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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Multi-scale wake structures around the dune
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Multi-scale wake structures around the dune

机译：沙丘周围的多尺度唤醒结构

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The three-dimensional wake structures behind a barchan dune model are investigated by the high-speed particle image velocimetry (PIV) at the Reynolds number of 5530. The measured velocity fields are first evaluated by time-averaged flow patterns and power spectra analysis. Then the one-dimensional orthogonal wavelet analysis is applied to reveal multi-scale turbulent structures and their corresponding second order statistics in the dune wake. The instantaneous multi-scale structures suggest that the large-scale structure is responsible for the formation of separation region. The intermediate-scale structure tends to be more active at the boundary of separation region, which may be due to the secondary vortex movement caused by the interactions between the wake and main flow. The appearance of small-scale vortices at the downstream of separation region indicates the breakdown process of large-scale vortices. The Reynolds stress and kinetic energy distribution suggest that the large-scale structures dominate the generation of turbulence in the dune wake. The lower kinetic energy contained in intermediate- and small- scale structures is considered to be related to smaller-scale interactions that reflect energy cascading phenomenon. The Reynolds shear stresses distributions suggest that the intermediate-scale structures also make significance in the separated boundary layer. As for small-scale structure, it is worthy to note that a region of high Reynolds shear stresses with an opposite sign is observed around the dune crest. The cross-correlation function of multi-scale structures suggest the quasi-periodicity of large-scale structure. The intermediate-scale structures also show a certain periodicity, however, such structures tend to be more unstable and the strength of them reduces as they travel downstream. When decreasing to small-scale, the vortical structures decays quickly at the downstream with larger convective velocity. This may indicate the breakdown process
机译：在雷诺数5530的高速粒子图像速度（PIV）研究了Barchan Dune模型背后的三维唤醒结构。首先通过时间平均的流动模式和功率谱分析来评估测量的速度场。然后应用一维正交小波分析来揭示多尺度湍流结构及其在沙丘唤醒中的相应二阶统计。瞬时多尺度结构表明，大规模结构负责分离区域的形成。中间结构结构在分离区域的边界处趋于更活跃，这可能是由于由唤醒和主流之间的相互作用引起的次级涡流运动。分离区域下游的小型涡旋的外观表示大规模涡旋的击穿过程。雷诺的应力和动力学能量分布表明，大规模结构在沙丘唤醒中占据了湍流的产生。中间和小规模结构中包含的较低的动能被认为与反映能量级联现象反映的较小比例相互作用有关。雷诺剪切应力分布表明中间尺度结构在分离的边界层中也具有重要性。对于小规模的结构，值得注意的是，在沙丘嵴周围观察到具有相反标志的高雷诺兹剪切应力的区域。多尺度结构的互相关函数表明大规模结构的准周期性。中间尺度结构还显示出一定的周期性，然而，这种结构倾向于更不稳定，并且它们在下游行驶时减少了它们的强度。在减少小规模时，涡流结构在具有较大的对流速度的下游衰减。这可能表示击穿过程

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