Scaling and statistics of large-defect adverse pressure gradient turbulent boundary layers
Scaling and statistics of large-defect adverse pressure gradient turbulent boundary layers
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DOI：
10.1016/j.ijheatfluidflow.2016.03.004
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发表时间：
2016-06-01
影响因子：
2.6
通讯作者：
Soria, J.
中科院分区：
文献类型：
--
作者：
Gungor, A. G.;Maciel, Y.;Soria, J.
本文的目的是测试相似定律和尺度思想，并使用六个实验和数值数据库（包括强减速非平衡湍流边界层的新直接数值模拟）来表征大缺陷逆压梯度湍流边界层的湍流行为。在后一种流动中，在中等雷诺数下，平均速度分布在整个内部区域（包括粘性底层）中偏离壁的经典定律，并且它们不遵循对数定律。然而，与解释粘性底层压力梯度的壁扩展定律非常吻合。当速度缺陷很重要时，雷诺应力分量在粘性子层中不是自相似的，但它们与压力粘性尺度相当好。在外部区域对六种不同的流动进行了详细比较。为了进行这种比较，引入了类似于通常定义的自由剪切层速度尺度的外部区域速度尺度。结果发现，所研究的大缺陷边界层上半部分的单点速度统计与混合层的速度统计相似：平均速度缺陷、雷诺应力、湍流动能收支、uv相关因子和结构参数-<uv>/2k。湍流产生和雷诺应力的主峰大致位于边界层的中间。 uv 相关因子的分布表明，随着平均速度缺陷的增加，尤其是在壁附近，u 和 v 在整个边界层中的相关性降低。大缺陷不平衡边界层的结构参数较低，与大缺陷平衡流和混合层类似，并且随着平均速度缺陷的增加而减小。研究发现，所有分析的大速度缺陷边界层从平均流中提取湍流能量的效率均低于零压力梯度湍流边界层，甚至在整个外部区域也是如此。 (C) 2016 Elsevier Inc. 保留所有权利。
The purpose of this article is to test similarity laws and scaling ideas, as well as characterize turbulence behaviour of large-defect adverse-pressure gradient turbulent boundary layers using six experimental and numerical databases including a new direct numerical simulation of a strongly decelerated non-equilibrium turbulent boundary layer. In the latter flow, at a moderate Reynolds number, the mean velocity profiles depart from the classical law of the wall throughout the inner region including in the viscous sublayer and they do not follow the log law. However, the agreement is excellent with the extended law of the wall that accounts for the pressure gradient for the viscous sublayer. The Reynolds stress components are not self-similar in the viscous sublayer when the velocity defect is important, but they scale reasonably well with the pressure-viscous scales.Detailed comparisons of the six different flows are made in the outer region. In order to do such comparisons, an outer region velocity scale analogous to the commonly defined free shear layer velocity scales is introduced. It is found that the investigated one-point velocity statistics in the upper half of large-defect boundary layers resemble those of a mixing layer: mean velocity defect, Reynolds stresses, turbulent kinetic energy budgets, uv correlation factor and structure parameter -< uv >/2k. The dominant peaks of turbulence production and Reynolds stresses are located roughly in the middle of the boundary layer. The profiles of the uv correlation factor reveal that u and v become less correlated throughout the boundary layer as the mean velocity defect increases, especially near the wall. The structure parameter is low in the large-defect disequilibrium boundary layers, similar to large-defect equilibrium flows and mixing layers and decreases as the mean velocity defect increases. All large-velocity-defect boundary layers analysed are found to be less efficient in extracting turbulent energy from the mean flow than zero-pressure-gradient turbulent boundary layers, even throughout the outer region. (C) 2016 Elsevier Inc. All rights reserved.