Turbulence and wall shear stress in unsteady internal flows with rough surfaces

粗糙壁面稳定流的基本流动物理知识通过实验和最近的大涡模拟（LES）和直接数值模拟（DNS）的高级数值模拟稳步发展。存在用于计算摩擦的有根据的工程方法。相比之下，非定常流动和摩擦粗糙的墙壁的研究是非常有限的，主要局限于明渠振荡流，主要是出于应用于海浪下的泥沙输运。对于内部流动（管道和导管流动），目前对非定常流动的理解和预测非定常摩擦的实际工程模型主要限于光滑壁条件，尽管大多数内部非定常流动发生在粗糙边界上。在光滑和粗糙壁面流动中，近壁面结构的流动和湍流之间存在基本差异，这使得粗糙壁面上的非定常流动动力学极有可能与光滑壁面上的非定常流动动力学显著不同，并且与光滑壁面上的非定常流动相关的结果在多大程度上适用于粗糙壁面条件尚不清楚。这种知识差距阻碍了从开发管道泄漏检测的先进方法和防止铁路隧道声震到优化水电和核电系统控制的应用。拟议的研究的目的是促进理解湍流和壁面剪切应力在非定常内部流粗糙表面，从而通过实验，数值和理论研究的综合方案，支持工程模型的发展。使用DNS/LES的数值模拟将生成关于湍流行为的非常详细的信息，特别是在粗糙度元件下方延伸的近壁区域中，但仅适用于低雷诺数和高相对粗糙度的条件，因为所需的计算资源在这些条件之外呈指数级增加。将进行补充实验，以产生涵盖更大范围的流动条件的数据，更直接地与实际应用相关。将分析计算和实验数据，以量化粗糙表面上非定常流中的湍流动力学和壁面剪应力。

Knowledge of the fundamental flow physics for steady flow over rough-walls has progressed steadily through experiments, and more recently through advanced numerical simulations using Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). Well-founded engineering methods exist for calculating friction. In contrast, the study of unsteady flow and friction over rough walls is very limited and is mostly confined to open channel oscillatory flow, largely motivated by application to sediment transport under sea waves. For internal flows (pipe and duct flow), present understanding of unsteady flow and practical engineering models for predicting unsteady friction are limited primarily to smooth wall conditions and this despite the fact that most internal unsteady flows occur over rough boundaries. There are basic differences between the near-wall structure of flow and turbulence in smooth and rough wall flows which make it highly likely that unsteady flow dynamics over rough walls are significantly different from those over smooth walls, and the extent to which results relating to unsteady flow over smooth walls apply to rough wall conditions is unknown. This knowledge gap handicaps applications ranging from the development of advanced methods of leak detection in pipelines and the prevention of sonic booms from railway tunnels to optimising the control of hydro and nuclear power systems. The aim of the proposed research is to advance understanding of turbulence and wall shear stress in unsteady internal flows over rough surfaces, thereby underpinning the development of engineering models through an integrated programme of experimental, numerical and theoretical studies. The numerical simulations using DNS/LES will generate very detailed information on the turbulent flow behaviour, especially in the near-wall region extending below the roughness elements, but only for conditions of low Reynolds number and high relative roughness since computing resources required increase exponentially beyond these conditions. Complementary experiments will be carried out to produce data covering a greater range of flow conditions, more directly relevant to practical applications. Computational and experimental data will be analysed to quantify turbulence dynamics and wall shear stress in unsteady flows over rough surfaces.