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A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

机译：风洞研究理想化城市表面上的水流，并进行粗糙度次层校正

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摘要

Dynamics in the roughness (RSLs) and inertial (ISLs) sublayers in the turbulent boundary layers (TBLs) over idealised urban surfaces are investigated analytically and experimentally. In this paper, we derive an analytical solution to the mean velocity profile, which is a continuous function applicable to both RSL and ISL, over rough surfaces in isothermal conditions. Afterwards, a modified mixing-length model for RSL/ISL transport is developed that elucidates how surface roughness affects the turbulence motions. A series of wind tunnel experiments are conducted to measure the vertical profiles of mean and fluctuating velocities, together with momentum flux over various configurations of surface-mounted ribs in cross flows using hot-wire anemometry (HWA). The analytical solution agrees well with the wind tunnel result that improves the estimate to mean velocity profile over urban surfaces and TBL dynamics as well. The thicknesses of RSL and ISL are calculated by monitoring the convergence/divergence between the temporally averaged and spatio-temporally averaged profiles of momentum flux. It is found that the height of RSL/ISL interface is a function of surface roughness. Examining the direct, physical influence of roughness elements on near-surface RSL flows reveals that the TBL flows over rough surfaces exhibit turbulence motions of two different length scales which are functions of the RSL and ISL structure. Conclusively, given a TBL, the rougher the surface, the higher is the RSL intruding upward that would thinner the ISL up to 50 %. Therefore, the conventional ISL log-law approximation to TBL flows over urban surfaces should be applied with caution.
机译：通过分析和实验研究了理想城市表面上湍流边界层（TBL）中粗糙度（RSLs）和惯性（ISLs）子层的动力学。在本文中，我们导出了平均速度曲线的解析解，该曲线是在等温条件下在粗糙表面上适用于RSL和ISL的连续函数。之后，开发了用于RSL / ISL传输的改进混合长度模型，该模型阐明了表面粗糙度如何影响湍流运动。使用热线风速仪（HWA）进行了一系列风洞实验，以测量平均速度和波动速度的垂直轮廓，以及横流中表面安装肋的各种配置上的动量通量。解析解与风洞结果非常吻合，风洞结果改进了对城市表面的平均速度分布和TBL动力学的估计。 RSL和ISL的厚度是通过监视动量通量的时间平均和时空平均轮廓之间的收敛/发散来计算的。发现RSL / ISL界面的高度是表面粗糙度的函数。检查粗糙元素对近表面RSL流的直接物理影响，发现在粗糙表面上的TBL流表现出两种不同长度尺度的湍流运动，这是RSL和ISL结构的函数。最后，给定了TBL，表面越粗糙，RSL向上侵入的程度就越高，这会使ISL变薄到50％。因此，应谨慎对待城市表面上TBL流量的常规ISL对数定律。

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  • 来源
    《Theoretical and applied climatology》 |2017年第2期|305-320|共16页
  • 作者

    Ho Yat-Kiu; Liu Chun-Ho;

  • 作者单位

    Univ Hong Kong, Dept Mech Engn, 7-F Haking Wong Bldg,Pokfulam Rd, Pokfulam, Hong Kong, Peoples R China;

    Univ Hong Kong, Dept Mech Engn, 7-F Haking Wong Bldg,Pokfulam Rd, Pokfulam, Hong Kong, Peoples R China;

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