Spatial development of a turbulent boundary layer subjected to freestream turbulence
Spatial development of a turbulent boundary layer subjected to freestream turbulence
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DOI：
10.1017/jfm.2020.967
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发表时间：
2021-01-25
影响因子：
3.7
通讯作者：
Hearst, R. Jason
中科院分区：
文献类型：
--
作者：
Jooss, Yannick;Li, Leon;Hearst, R. Jason
在水槽中，对摩擦雷诺数为的自由湍流边界层的空间发展进行了实验研究。四个不同的FST强度与一个活跃的网格，范围从低湍流参考情况。壁正常速度扫描进行激光多普勒测速仪在三个位置下游的网格。随着流动的发展，有两种对抗性的影响：TBL增长，而FST衰减。虽然以前的研究表明尾流区的TBL抑制FST，目前的测量表明，尾流恢复足够远的下游。对于低水平的FST，近壁方差峰值增长作为一个移动下游，而高FST的结果在一个最初的高方差峰值随流向位置衰减。这些结果反映在谱图的演变中，其中低FST导致随着流动演变出现外谱峰，而高FST在空间中看到初始高的外谱峰衰减。这一发现意义重大，因为它表明FST不会在TBL自然进化之前永久成熟。最后，它明确表明，它是不够的，仅由传统的参数，如表征的TBL，但也必须考虑的水平FST和两个流的演变。
The spatial development of a turbulent boundary layer (TBL) subjected to freestream turbulence (FST) is investigated experimentally in a water channel for friction Reynolds numbers up to . Four different FST intensities are generated with an active grid, ranging from a low-turbulence reference case to . Wall-normal velocity scans are performed with laser doppler velocimetry at three positions downstream of the grid. There are two combating influences as the flow develops: the TBL grows while the FST decays. Whilst previous studies have shown the wake region of the TBL is suppressed by FST, the present measurements demonstrate that the wake recovers sufficiently far downstream. For low levels of FST, the near-wall variance peak grows as one moves downstream, whereas high FST results in an initially high variance peak that decays with streamwise position. These results are mirrored in the evolution of the spectrograms, where low FST results in the emergence of an outer spectral peak as the flow evolves, while high FST sees an initially high outer spectral peak decay in space. This finding is significant as it suggests the FST does not permanently mature the TBL ahead of its natural evolution. Finally, it is explicitly demonstrated that it is not sufficient to characterize the TBL solely by conventional parameters such as , but that the level of FST and the evolution of the two flows must also be considered.