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.

实验室尺度平滑的开通通道流可以被认为是液压工程中最简单的流场。 但是，该流动表现出许多在复杂湍流中发生的现象。为了了解复杂的流场，研究人员研究了标准平滑床流对变化边界条件的响应，这些条件以许多不同形式（例如床粗糙度变化）。 还值得注意的是，从实验室尺度上非常简单的流量建立的经验关系通常被采用远远超出其在更复杂的流场中的有效性范围。 这尤其令人不安，因为在使用经验关系的商业计算代码的使用中存在扩散。 例如，有大量的工作试图将河床形成粗糙度与经典实验中采用的沙子粗糙度相关联。大多数实用的开放通道流都发生在带有或没有渗漏的粗糙（移动/固定）床上（吸力/注射）。 虽然平均速度和剪切应力的分布有充分的文献证明，但湍流结构的作用却鲜为人知。 在建模实际流动时会出现几个关键问题。 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运输的较大湍流涡流的大小和频率？ 在存在渗漏和床迁移的情况下，连贯结构的常规法律和作用如何改变？ 本提案将通过对所选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，并具有定义明确的流动条件，包括渗透效应。 该提案的目的是研究瞬时，随时间发展的相干结构，以及它们如何受到床/游离表面的接近性影响。 将使用正交分解，动量分析和条件象限分析来检查速度场。 温莎大学的最先进的实验设施和数值代码的可用性使这项研究成为可能。