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Large-eddy simulation study of the logarithmic law for second- and higher-order moments in turbulent wall-bounded flow

机译:湍流边界流中二阶和高阶矩对数律的大涡模拟研究

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摘要

The logarithmic law for the mean velocity in turbulent boundary layers has long provided a valuable and robust reference for comparison with theories, models and large-eddy simulations (LES) of wall-bounded turbulence. More recently, analysis of high-Reynolds-number experimental boundary-layer data has shown that also the variance and higher-order moments of the streamwise velocity fluctuations u ′+ display logarithmic laws. Such experimental observations motivate the question whether LES can accurately reproduce the variance and the higher-order moments, in particular their logarithmic dependency on distance to the wall. In this study we perform LES of very high-Reynolds-number wall-modelled channel flow and focus on profiles of variance and higher-order moments of the streamwise velocity fluctuations. In agreement with the experimental data, we observe an approximately logarithmic law for the variance in the LES, with a ‘Townsend–Perry’ constant of A 1 ≈1.25 . The LES also yields approximate logarithmic laws for the higher-order moments of the streamwise velocity. Good agreement is found between A p , the generalized ‘Townsend–Perry’ constants for moments of order 2p , from experiments and simulations. Both are indicative of sub-Gaussian behaviour of the streamwise velocity fluctuations. The near-wall behaviour of the variance, the ranges of validity of the logarithmic law and in particular possible dependencies on characteristic length scales such as the roughness length z 0 , the LES grid scale Δ , and subgrid scale mixing length C s Δ are examined. We also present LES results on moments of spanwise and wall-normal fluctuations of velocity
机译:湍流边界层中平均速度的对数定律长期以来为与壁面湍流的理论,模型和大涡模拟(LES)进行比较提供了宝贵而强大的参考。最近,对高雷诺数实验边界层数据的分析表明,沿流速度波动u′+的方差和高阶矩也显示了对数律。这样的实验观察引发了这样一个问题,即LES是否可以准确地再现方差和高阶矩,尤其是它们对距壁的距离的对数依赖性。在这项研究中,我们执行了非常高的雷诺数壁模拟通道流的LES,并着重研究了流向速度波动的方差和高阶矩剖面。与实验数据一致,我们观察到LES中方差的近似对数律,“ Townsend-Perry”常数为A 1≈1.25。 LES还为流向速度的高阶矩产生近似对数定律。通过实验和模拟,在2 p阶矩的广义“ Townsend-Perry”常数A p之间发现了很好的一致性。两者都表示沿流速度波动的次高斯行为。检查方差的近壁行为,对数律的有效性范围,尤其是对特征长度尺度(例如粗糙度长度z 0,LES网格尺度Δ和子网格尺度混合长度C sΔ)的可能依赖关系。我们还给出了翼展方向矩和壁面法向速度波动的LES结果

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