Abstract A turbulent boundary layer under the impact of a strong adverse pressure gradient up to flow separation is investigated experimentally at Reynolds numbers up to Re τ = 12 , 000 , with the aim to analyse and characterise the interaction between large-scale coherent turbulent structures and a separated flow region. It is shown that the dynamics of the separation line in space and time are strongly modulated by the low frequency large-scale flow motions. Using a conditional comparison of mean flow parameters, it is shown that high-momentum large-scale motions are able to shift the point of separation downstream while the opposite is true for low-momentum large-scale motions. This interaction has a significant impact on the temporal dynamics of the separation line. The spatial frequencies observable along the line of separation on the other hand are determined by the spanwise arrangement of high and low-momentum large-scale motions. Finally, it is demonstrated that the separated region does not have a major influence on the mean boundary layer thickness in contrast to the mean flow velocity and spatial scales of coherent structures which are visibly influenced in the vicinity of the separated region.

中文翻译：

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逆压力梯度下湍流边界层中的大规模相干运动直至流动分离

摘要 以高达 Re τ = 12 , 000 的雷诺数实验研究了在强逆压力梯度作用下直至流动分离的湍流边界层，旨在分析和表征大尺度相干湍流结构与流动分离之间的相互作用。分离的流动区域。结果表明，分离线在空间和时间上的动力学受到低频大尺度流动运动的强烈调制。使用平均流动参数的条件比较，表明高动量的大规模运动能够将分离点向下游移动，而低动量的大规模运动则相反。这种相互作用对分离线的时间动态有显着影响。另一方面，沿分离线可观察到的空间频率由高动量和低动量大尺度运动的展向排列决定。最后，证明了与在分离区域附近明显影响的相干结构的平均流速和空间尺度相比，分离区域对平均边界层厚度没有重大影响。