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.

实验室规模的光滑明渠流可以认为是水利工程中最简单的流场。 然而，这种流动表现出复杂湍流中发生的许多现象。为了了解复杂的流场，研究人员研究了标准平滑床流对以多种不同形式施加的边界条件变化（例如床层粗糙度的变化）的响应。 还值得注意的是，在实验室规模上从非常简单的流动建立的经验关系常常在更复杂的流场中远远超出其既定的有效性范围。 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已经激增。 例如，有大量工作试图将河床形状粗糙度与经典实验中使用的沙粒粗糙度联系起来。大多数实际的明渠流动发生在粗糙（移动/不动）床上，有或没有渗漏（抽吸/注入）。 虽然平均速度和剪切应力的分布已有详细记录，但湍流结构的作用却鲜为人知。 在对实际流程进行建模时出现了几个关键问题。 其中包括：粗糙度几何形状（高度、间距、密度等）如何确定负责大部分传输的较大湍流涡流的大小和频率？ 在存在渗漏和床层流动性的情况下，相干结构的传统定律和作用如何改变？ 本提案将通过对选定的粗糙度几何形状进行数值模拟和实验室实验，以及明确定义的流动条件（包括渗流效应）来系统地解决这些和其他重要问题。 该提案的目标是研究瞬时的、随时间演化的相干结构以及它们如何受到床/自由表面接近度的影响。 将使用适当正交分解、动量分析和条件象限分析来检查速度场。 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。