Revisiting “bursts” in wall-bounded turbulent flows
Revisiting “bursts” in wall-bounded turbulent flows
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DOI：
10.1103/physrevfluids.8.044606
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发表时间：
2023-01
影响因子：
2.7
通讯作者：
S. Chowdhuri;T. Banerjee
中科院分区：
文献类型：
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作者：
S. Chowdhuri;T. Banerjee
众所周知，湍流信号会表现出类似爆发的活动，这会影响大尺度和小尺度流动的湍流统计。在我们的研究中，我们从基于事件的框架的角度来解决这个问题，其中突发事件的大小和持续时间都在多个尺度上进行研究。为了说明我们的方法并评估对雷诺数的依赖性，我们使用两个数据集 - 来自墨尔本风洞和 SLTEST - 大气表层实验。我们表明，一个指数，即突发指数，可以成功地用来描述湍流爆发的多尺度性质，同时考虑小尺度间歇效应。通过该指数，我们证明，无论雷诺数如何，瞬时速度方差和动量通量信号中是否存在大幅波动是由流动中的相干结构控制的。关于小尺度湍流，在研究二阶流向速度增量的突发特征的尺度演化时，注意到雷诺数依赖性。具体到风洞数据集，流向速度增量信号的突发指数表现出对高度的强烈依赖性，并且随着尺度的增加而减小，在与耗散结构相当的尺度上获得最大值。然而，这些特征在大气流动中几乎不存在。总而言之，这项研究为评估突发对任何指定流动规模的湍流统计的影响铺平了一种新的方法。
Turbulent signals are known to exhibit burst-like activities, which affect the turbulence statistics at both large and small scales of the flow. In our study, we pursue this problem from the perspective of an event-based framework, where bursting events are studied across multiple scales in terms of both their size and duration. To illustrate our method and assess any dependence on the Reynolds number, we use two datasets - from the Melbourne wind tunnel and from SLTEST - an atmospheric surface layer experiment. We show that an index, namely the burstiness index, can be used successfully to describe the multi-scale nature of turbulent bursting while accounting for the small-scale intermittency effects. Through this index, we demonstrate that irrespective of the Reynolds number, the presence of large amplitude fluctuations in the instantaneous velocity variance and momentum flux signals are governed by the coherent structures in the flow. Concerning small-scale turbulence, a Reynolds number-dependence is noted while studying the scale-wise evolution of the burstiness features of second-order streamwise velocity increments. Specific to the wind-tunnel dataset, the burstiness index of streamwise velocity increment signal displays a strong dependence on height and also decreases as the scales increase with the maximum being obtained at scales comparable to the dissipative structures. However, such features are nearly absent in the atmospheric flows. To conclude, this research paves a novel way to evaluate the effect of bursts on the turbulence statistics at any specified scale of the flow.