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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 >Low- and high-speed structures in the outer region of an adverse-pressure-gradient turbulent boundary layer
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Low- and high-speed structures in the outer region of an adverse-pressure-gradient turbulent boundary layer

机译：负压梯度湍流边界层外部区域的低速和高速结构

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摘要

Large- and very large-scale structures in the form of elongated regions of low and high streamwise momentum have been studied in the outer region of a turbulent boundary layer subjected to a strong adverse pressure gradient. Large sets of streamwise-spanwise instantaneous velocity fields are acquired by particle image velocimetry at three wall-normal positions (0.2 δ, 0.5 δ, 0.8 δ) at three different streamwise locations and at 0.1 δ at the last streamwise location which allows us to study the wall-normal and streamwise variations of the structures. Subsequently, a pattern-recognition method and a classification scheme are employed in order to detect, classify and characterize the structures in an efficient and rigorous manner. Like in the case of zero-pressure-gradient turbulent boundary layers, long meandering streaky regions of low and high momentum are observed in the outer region of the present flow but they appear less frequently; especially in the lower part (at 0.1 δ and 0.2 δ) of the large-velocity-defect zone, i.e. near detachment. The dimensions of these large structures scale on boundary-layer thickness (δ) and are generally comparable to those previously reported for such structures in the overlap region of zero-pressure-gradient turbulent boundary layers. Interestingly, the adverse pressure gradient does not significantly affect the dimensions and arrangement of the large-scale structures in the upper part (at 0.5 δ and 0.8 δ) a segment of the outer region where the scaled Reynolds stresses also remain fairly self-similar.
机译：在湍流边界层的外部区域，研究了承受强烈逆压梯度的，呈低，高流向动量的细长区域形式的大型和超大型结构。通过粒子图像测速法在三个不同的流向位置的三个壁法向位置（0.2δ，0.5δ，0.8δ）和最后一个流向位置的0.1δ处获取了大的流向跨瞬时速度场。结构的墙体法向和沿河向变化。随后，采用模式识别方法和分类方案以便以有效且严格的方式检测，分类和表征结构。像零压力梯度湍流边界层的情况一样，在当前流动的外部区域观察到了低动量和高动量的长曲折条纹区，但它们出现的频率较低。特别是在大速度缺陷区的下部（在0.1δ和0.2δ处），即在分离附近。这些大型结构的尺寸在边界层厚度（δ）上成比例，并且通常与先前在零压力梯度湍流边界层的重叠区域中针对此类结构所报道的尺寸相当。有趣的是，不利的压力梯度不会显着影响大型结构在上部区域（0.5δ和0.8δ）处外部区域的尺寸和排列，在该区域中按比例缩放的雷诺应力也保持相当自相似。

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