ABSTRACT Adverse-pressure-gradient turbulent boundary layer flow was inspected at Reynolds number based on momentum thickness, , using particle image velocimetry in a refractive-index-matching flume. Proper orthogonal decomposition was used to quantify the effect of large-scale motions on the Reynolds stresses at the onset of separation and within the separated flow. Results show that approximately of the Reynolds shear stress, , is due to large-scale motions containing of the turbulence kinetic energy at the tested Reynolds number. The decomposed velocity field revealed that only the first of the modes is sufficient to recover of the turbulence kinetic energy. In this partition, the large-scale motion contribution to the streamwise component of the Reynolds normal stress, , is about and continues to grow with flow separation. In addition, the large- and small-scale motions equally contributed to the vertical component of the Reynolds normal stress, , and the contribution of the large-scale motions increased as the flow separated. Overall, results emphasise the significant impact of the large-scale motions on the Reynolds stresses in the separated flow, which may impact flow control strategies.

中文翻译：

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关于分离的湍流边界层流中的大尺度和小尺度运动

摘要 基于动量厚度，使用粒子图像测速仪在折射率匹配槽中以雷诺数检查逆压力梯度湍流边界层流动。适当的正交分解用于量化大规模运动对分离开始时和分离流内的雷诺应力的影响。结果表明，雷诺剪应力的近似值是由于包含测试雷诺数下的湍流动能的大规模运动。分解的速度场表明，只有第一种模式足以恢复湍流动能。在这个分区中，对雷诺法向应力流向分量的大规模运动贡献大约是并继续随着流动分离而增长。此外，大尺度和小尺度运动对雷诺法向应力的垂直分量的贡献相等，并且随着流动的分离，大尺度运动的贡献增加。总体而言，结果强调了大规模运动对分离流动中雷诺应力的显着影响，这可能会影响流动控制策略。