Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers
Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers
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高雷诺数下表面条件从粗糙到平滑变化的湍流边界层的实验研究
DOI：
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发表时间：
2021
影响因子：
3.7
通讯作者：
N. Hutchins
中科院分区：
文献类型：
--
作者：
Mogeng Li;C. D. de Silva;D. Chung;D. Pullin;I. Marusic;N. Hutchins
摘要：本研究提出了一个实验数据集，记录了粗糙到光滑表面转变下游的湍流边界层的演变。为了研究上游流动条件的影响，进行了两组实验。对于 Group-Re 情况，在粗糙表面上保持名义上恒定的粘性尺度等效砂粒粗糙度 $k_{s0}^{+}约 160$，而摩擦雷诺数 $Re_{ au 0}$ 范围为 7100 到 21 000。对于 Group-ks 情况，$Re_{ au 0}保持约 14,000$，而$k_{s0}^{+}$ 范围为 111 至 228。下游光滑表面上的壁剪应力是使用油膜干涉仪直接测量的，以纠正先前报道的表面摩擦系数恢复趋势的不确定性。在粗糙度转变后的早期发展中，内层中的流动与壁剪应力不平衡。这与将平均速度剖面建模为内层高度下方和上方的两个对数定律的常见做法相冲突，正如 Elliott 首次提出的那样（Trans. Am. Geophys. Union，第 39 卷，1958 年，第 1048-1054 页）。作为解决方案，当前数据用于通过混合相应的粗糙壁和光滑壁轮廓来半经验地模拟恢复平均速度。过度能量的大规模运动在能谱的近壁区域留下了强烈的足迹，其频率和幅度分别依赖于 $Re_{ au 0}$ 和 $k_{s0}^{+}$。近壁小尺度的能量分布大多不受具有粗糙壁特征的外流的影响，这可以用作提取局部摩擦速度的替代措施。
Abstract This study presents an experimental dataset documenting the evolution of a turbulent boundary layer downstream of a rough-to-smooth surface transition. To investigate the effect of upstream flow conditions, two groups of experiments are conducted. For the Group-Re cases, a nominally constant viscous-scaled equivalent sand grain roughness $k_{s0}^{+}approx 160$ is maintained on the rough surface, while the friction Reynolds number $Re_{ au 0}$ ranges from 7100 to 21 000. For the Group-ks cases, $Re_{ au 0}approx 14,000$ is maintained while $k_{s0}^{+}$ ranges from 111 to 228. The wall-shear stress on the downstream smooth surface is measured directly using oil-film interferometry to redress previously reported uncertainties in the skin-friction coefficient recovery trends. In the early development following the roughness transition, the flow in the internal layer is not in equilibrium with the wall-shear stress. This conflicts with the common practise of modelling the mean velocity profile as two log laws below and above the internal layer height, as first proposed by Elliott (Trans. Am. Geophys. Union, vol. 39, 1958, pp. 1048–1054). As a solution to this, the current data are used to model the recovering mean velocity semi-empirically by blending the corresponding rough-wall and smooth-wall profiles. The over-energised large-scale motions leave a strong footprint in the near-wall region of the energy spectrum, the frequency and magnitude of which exhibit dependence on $Re_{ au 0}$ and $k_{s0}^{+}$, respectively. The energy distribution in near-wall small scales is mostly unaffected by the presence of the outer flow with rough-wall characteristics, which can be used as a surrogate measure to extract the local friction velocity.
壁粗糙度发生阶跃变化后湍流边界层的发展
影响因子：
3.7
作者：
Hanson R
通讯作者：
Hanson R