On the validity of the quasi-steady-turbulence hypothesis in representing the effects of large scales on small scales in boundary layers
On the validity of the quasi-steady-turbulence hypothesis in representing the effects of large scales on small scales in boundary layers
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DOI：
10.1063/1.4944735
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发表时间：
2016-04
影响因子：
4.6
通讯作者：
L. Agostini;M. Leschziner
中科院分区：
文献类型：
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作者：
L. Agostini;M. Leschziner
在近壁湍流中大尺度/小尺度相互作用的上下文中所理解的“准定常假设”是基于这样的假设：壁附近的小尺度在很短的时间尺度内对由能量大尺度施加给它们的变化作出反应，这些能量大尺度的长度尺度至少相差一个数量级，并且其能量在对数律层的中间到外部达到最大值。这一假设的一个关键统计表现是，用大尺度的壁摩擦速度足迹来缩放小尺度运动，使得小尺度统计具有普遍性。本文通过参考雷诺数为4200的直接数值模拟（DNS）数据对这一假设进行了检验，并采用经验模态分解方法对大尺度/小尺度进行了分离。检查的流量特性包括平均速度，二阶矩，联合概率密度函数，和偏度。结果表明，该假设的有效性取决于部分…
The “quasi-steady hypothesis,” as understood in the context of large-scale/small-scale interactions in near-wall turbulence, rests on the assumption that the small scales near the wall react within very short time scales to changes imposed on them by energetic large scales whose length scales differ by at least one order of magnitude and whose energy reaches a maximum in the middle to the outer portion of the log-law layer. A key statistical manifestation of this assumption is that scaling the small-scale motions with the large-scale wall-friction-velocity footprints renders the small-scale statistics universal. This hypothesis is examined here by reference to direct numerical simulation (DNS) data for channel flow at Reτ ≈ 4200, subjected to a large-scale/small-scale separation by the empirical mode decomposition method. Flow properties examined include the mean velocity, second moments, joint probability density functions, and skewness. It is shown that the validity of the hypothesis depends on the part...