发表机构
UCLouvain（法语鲁汶大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用时间发展湍流边界层框架，验证了稳定分层下Monin-Obukhov相似性理论在更广范围内的适用性，并提出经验修正以准确预测壁面摩擦系数。
AI 中文摘要
稳定分层的壁面湍流控制着许多环境和工程流动的动力学。一个关键挑战是表征分层如何改变平均和湍流剖面。Monin-Obukhov相似性理论（MOST）是主要的建模框架，尽管它很少在广泛的分层水平范围内针对受控良好的直接数值模拟（DNS）数据进行严格验证。在本研究中，我们利用时间发展湍流边界层（TTBL）框架来研究从弱稳定到极稳定状态的分层湍流边界层，涵盖一系列雷诺数和理查森数，并将浮力效应与流动旋转等其他机制隔离开来。我们证明TTBL设置忠实地再现了经典相似性理论结果，并且平均速度梯度的基于表面的标度在比先前报道更宽的$z/L$（$L$为Obukhov长度）范围内成立。这一结果归因于该典型流动中湍流剪切应力和热通量的相似衰减速率。接下来，我们表明，随着分层增强，平均速度剖面的截距增加，直到维持对数区所需的尺度分离无法再持续。我们提出了一个基于Obukhov长度的雷诺数对该截距位移的经验闭合。最后，提出并验证了对MOST对平均速度剖面贡献的简单阻尼，使得能够在所研究的各个状态下准确预测壁面摩擦系数（$C_f$）。
英文摘要
Stably stratified wall-bounded turbulence governs the dynamics of many environmental and engineering flows. A key challenge is characterizing how stratification modifies mean and turbulent profiles. Monin--Obukhov similarity theory (MOST) is the dominant modelling framework, although it has rarely been rigorously validated against well-controlled direct numerical simulation (DNS) data over a wide range of stratification levels. In this study, we exploit the temporally developing turbulent boundary layer (TTBL) framework to investigate stratified turbulent boundary layers from the weakly stable to the very stable regime, spanning a range of Reynolds and Richardson numbers, and isolating the effects due to buoyancy from other mechanisms such as flow rotation. We demonstrate that the TTBL set-up faithfully reproduces classical similarity theory results and that surface-based scaling of the mean velocity gradient holds over a wider range of $z/L$ ($L$ being the Obukhov length) than previously reported. This result is attributed to the similar decay rate of turbulent shear stress and heat flux in this canonical flow. Next, we show that, as stratification intensifies, the intercept of the mean velocity profile increases, until the separation of scales required for a logarithmic region to exist can no longer be sustained. We propose an empirical closure for this intercept shift in terms of the Reynolds number based on the Obukhov length. Finally, a simple damping of the MOST contribution to the mean velocity profile is proposed and validated, enabling accurate prediction of the wall friction coefficient ($C_f$) across the investigated regimes.
Comments27 pages, 17 figures
