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Statistical analysis of vortical structures in turbulent boundary layer over directional grooved surface pattern with spanwise heterogeneity

机译：跨越边界层涡流结构与跨向沟槽表面图案的涡流结构统计分析

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摘要

We examine the turbulent boundary layers developing over convergent-divergent riblets (C-D riblets) with three different heights (h(+) = 8, 14, and 20) at Re-theta = 723 using particle image velocimetry. It is observed that although a logarithmic region presents in the velocity profiles over the converging and diverging line, Townsend's outer-layer similarity hypothesis is invalid. Compared to the smooth-wall case, C-D riblets with a height of 2.4% of the smooth-wall boundary layer thickness can cause a significant increase in the turbulence production activities over the converging region, as evidenced by a more than 50% increase in the turbulent shear stress and in the population of prograde and retrograde spanwise vortices. In contrast, the impact of riblets on the diverging region is much smaller. The slope of vortex packets becomes steeper, and they are more streamwise stretched in the outer layer over the diverging region, whereas their shape and orientation is less affected over the converging region. Furthermore, the number of uniform momentum zones across the boundary layer increases over the converging region, causing a reduction in the thickness of uniform momentum zones in the outer part of the boundary layer. Overall, while an increased riblet height affects a large portion of the boundary layer away from the wall over the converging region, the impact on the diverging region is largely confined within the near-wall region. Such distinct differences in the response of the boundary layer over the diverging and converging region are attributed to the opposite local secondary flow motion induced by C-D riblets. Published under license by AIP Publishing.
机译：我们检查紊流附面层用在重新-θ= 723三个不同高度（H（+）= 8，14，和20），使用粒子图像测速显影过度会聚 - 发散肋（C-d肋）。可以观察到，虽然在速度分布上会聚和发散线的对数区的礼物，汤森的外层相似的假设是无效的。相较于光滑壁的情况下，与光滑壁边界层的厚度的2.4％的高度CD肋可引起过会聚区域中的湍流生产活动显著增加，通过在增加超过50％所证明的湍流的剪切应力和在顺行和逆行翼展方向涡流的人口。相比之下，于发散区域的拉条的影响要小得多。涡流分组的斜率变得陡峭，并且它们在通过发散区域中的外层更流向拉伸，而它们的形状和取向的影响较小过会聚区域。此外，跨过会聚区域的边界层增大均匀动量区的数量，从而导致在边界层的外部部分均匀动量区域的厚度减小。总体而言，虽然增加的肋的高度影响边界层从所述壁在所述聚光区域远的大部分，在发散区域的影响在很大程度上近壁区域内限制。在过度发散和会聚的区域中的边界层的响应这样的明显的差异归因于由C-d肋引起的相对局部二次流运动。通过AIP发布在许可证下发布。

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  • 来源
    《Physics of fluids》 |2019年第8期|共17页
  • 作者

    Xu Fang; Zhong Shan; Zhang Shanying;

  • 作者单位

    Univ Manchester Sch Mech Aerosp &

    Civil Engn Manchester M13 9PL Lancs England;

    Univ Manchester Sch Mech Aerosp &

    Civil Engn Manchester M13 9PL Lancs England;

    Univ Manchester Sch Mech Aerosp &

    Civil Engn Manchester M13 9PL Lancs England;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 流体力学;
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