Advanced experiments and simulations to model coherent structures in shallow smooth and rough open channels

实验室尺度光滑明渠水流可以认为是水利工程中最简单的流场。 然而，这种流动表现出许多复杂湍流中出现的现象。为了理解复杂的流场，研究人员研究了标准光滑床流对以许多不同形式施加的变化边界条件（例如床粗糙度的变化）的响应。 同样值得注意的是，在实验室尺度上从非常简单的流动中建立的经验关系式，在更复杂的流场中经常被采用，远远超出它们所建立的有效范围。 这尤其令人不安，因为使用经验关系的商业计算代码的使用已经激增。 例如，有相当多的工作试图将河床形状粗糙度与经典实验中采用的沙粒粗糙度联系起来。大多数实际的明渠水流发生在粗糙（移动的/非移动的）河床上，有或没有渗流（吸入/注入）。 虽然平均速度和剪切应力的分布是有据可查的，湍流结构的作用是鲜为人知的。 在对实际流程建模时出现了几个关键问题。 这些问题包括：粗糙度几何形状（高度、间距、密度等）确定负责大量运输的较大湍流漩涡的大小和频率？ 在渗流和河床流动性存在的情况下，相干结构的传统定律和作用是如何被修改的？ 本提案将通过对选定的粗糙几何形状进行数值模拟和实验室实验，并在包括渗流效应在内的明确流动条件下，系统地解决这些问题和其他重要问题。 本建议的目标是研究瞬时的，随时间变化的相干结构，以及它们是如何受到床/自由表面的接近。 速度场将使用适当的正交分解，动量分析和条件象限分析进行检查。 温莎大学拥有最先进的实验设施和数字代码，使这项研究成为可能。

Laboratory scale smooth open channel flow can be considered to be the simplest flow field in hydraulic engineering. However, this flow exhibits many of the phenomena that occur in complex turbulent flows. To understand complex flow fields, researchers have studied the response of the standard smooth bed flow to changing boundary conditions which are imposed in many different forms (such as change in bed roughness). It is also noteworthy that empirical relations established from very simple flows at laboratory scales are often employed far beyond their established range of validity in the more complex flow fields. This is particularly disconcerting as there has been a proliferation in the use of commercial computational codes which use the empirical relations. For e.g., there is considerable work which attempts to relate river bed form roughness to sand grain roughness employed in classical experiments. Most practical open channel flows occur on rough (mobile/immobile) beds with or without seepage (suction/injection). While the distribution of the mean velocities and shear stress is well documented, the role of turbulent structures is less known. Several critical questions arise while modeling practical flows. These include: How does roughness geometry (height, spacing, density etc.) determine the size and frequency of the larger turbulent eddies responsible for bulk of the transport? How are the conventional laws and role of coherent structures modified in the presence of seepage and bed mobility? The present proposal will systematically address these and other important questions by conducting numerical simulation and laboratory experiments on selected roughness geometry with well defined flow conditions including seepage effects. The goal of this proposal is to study the instantaneous, time-evolving coherent structures and how they are affected by the proximity of the bed/free surface. The velocity fields will be examined using proper-orthogonal decomposition, momentum analysis, and conditional quadrant analysis. The study is made possible by the availability of state-of-the-art experimental facilities and numerical codes at the University of Windsor.