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

先进的实验和模拟，用于模拟浅层光滑和粗糙明渠中的相干结构

• 批准号: 183977-2008
• 负责人: Balachandar, Ramaswami
• 金额: $ 2.11万
• 依托单位: University of Windsor
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2012
• 资助国家: 加拿大
• 起止时间: 2012-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=505205
• 关键词: Advanced; experiments; simulations; model; coherent

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.

实验室规模的明渠光滑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在复杂的湍流中发生的现象。为了了解复杂的流场，研究人员研究了标准光滑床流对以多种不同形式施加的变化的边界条件(如床面粗糙度的变化)的响应。还值得注意的是，在实验室尺度上从非常简单的流动建立的经验关系往往远远超出了它们在更复杂的流动领域中的既定有效性范围。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激增。例如，有相当多的工作试图将河床形态粗糙度与经典实验中使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的(流动/固定)床上，有或没有渗漏(吸入/注入)。虽然平均速度和剪应力的分布已被很好地记录下来，但湍流结构的作用却鲜为人知。在对实际流程进行建模时，会出现几个关键问题。其中包括：粗糙度几何图形(高度、间距、密度等)如何确定造成大部分输送的较大湍流涡旋的大小和频率？在渗流和河床流动存在的情况下，相干结构的常规规律和作用是如何修改的？本提案将通过对选定的具有明确流动条件(包括渗流效应)的粗糙度几何形状进行数值模拟和实验室实验，系统地解决这些问题和其他重要问题。这一提议的目的是研究瞬时的、随时间演变的相干结构以及它们如何受到床层/自由表面接近的影响。速度场将使用本征正交分解、动量分析和条件象限分析进行检验。温莎大学最先进的实验设备和数字代码使这项研究成为可能。