Interaction of coherent flow structures in adverse pressure gradient turbulent boundary layers
Interaction of coherent flow structures in adverse pressure gradient turbulent boundary layers
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DOI：
10.1017/jfm.2019.408
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发表时间：
2019-06
影响因子：
3.7
通讯作者：
M. Bross;T. Fuchs;C. Kähler
中科院分区：
文献类型：
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作者：
M. Bross;T. Fuchs;C. Kähler
为了表征对数律区域内的近壁流动结构及其与大尺度运动的相互作用，在摩擦雷诺数Re_{\unicode[STIX]{x1 D 70 F}}=5000$下，在逆压梯度湍流边界层和零压梯度湍流边界层的近壁和对数律区域内进行了时间分辨的平面和体积流场测量。由于测量的高空间和时间分辨率，有可能分辨和识别区域$z/\unicode[STIX]{x1 D 6 FF}<0.15$或$z^{+}<350$中的均匀动量区，并将它们与壁面附近众所周知的相干流运动联系起来。时空的结果证实，湍流超结构有很强的影响，即使在非常近壁的流动运动，也可以在很长的时间序列中量化的时间和强度的交替出现。利用速度场的时间记录，还分析了粘性亚层中出现的罕见的局部分离事件。利用体积粒子跟踪测速技术，可以解决它们的三维拓扑和动力学问题。基于这些结果，推导出一个概念模型，该模型通过低动量湍流上层结构、近壁低速条纹和位于近壁区域的倾斜纵向和展向涡之间的复杂相互作用过程来解释它们的罕见发生、拓扑结构和动力学。
With the aim to characterize the near-wall flow structures and their interaction with large-scale motions in the log-law region, time-resolved planar and volumetric flow field measurements were performed in the near-wall and log-law region of an adverse pressure gradient turbulent boundary layer following a zero pressure gradient turbulent boundary layer at a friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}=5000$ . Due to the high spatial and temporal resolution of the measurements, it was possible to resolve and identify uniform-momentum zones in the region $z/\unicode[STIX]{x1D6FF}<0.15$ or $z^{+}<350$ and to relate them with well known coherent flow motions near the wall. The space–time results confirm that the turbulent superstructures have a strong impact even on the very near-wall flow motion and also their alternating appearance in time and intensity could be quantified over long time sequences. Using the time record of the velocity field, rare localized separation events appearing in the viscous sublayer were also analysed. By means of volumetric particle tracking velocimetry their three-dimensional topology and dynamics could be resolved. Based on the results, a conceptual model was deduced that explains their rare occurrence, topology and dynamics by means of a complex interaction process between low-momentum turbulent superstructures, near-wall low-speed streaks and tilted longitudinal and spanwise vortices located in the near-wall region.