Bedform related macroturbulence: topology and kinematics

与床型相关的宏观湍流：拓扑和运动学

基本信息

批准号：
NE/H012397/1
负责人：
Daniel Parsons
金额：
$ 5.35万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FH012397%2F1
关键词：
Bedform related macroturbulence topology kinematics

项目摘要

All rivers transport sediment both along their beds and suspended within the water column, with the material rolling along the bed often been sculpted into a range of forms by the water: one of the most common of these forms are dunes that may be generated in both sandy and gravelly sediment. Such dunes are nearly always present in alluvial channels and are one of the main ways in which the coarser sediment is transported by the flow. Many of the world's small and large rivers possess such dunes, which in big rivers may reach up to 6m high and tens or even hundreds of metres in length. Such dunes are generated by the turbulent flow but, once formed, begin to greatly disrupt the flow that is moving over them, thereby extracting energy from the flow in the resistance they offer to the passage of water, and creating large-scale turbulent eddies, or 'macroturbulence', within the flow. These large-scale eddies are very often visible as upwellings or 'boils' of fluid on the water surface of rivers, and are familiar to canoeists and boatmen. This turbulence itself can be responsible for suspending and transporting appreciable quantities of sediment and forms part of a complex series of 'feedback' processes between fluid flow, sediment movement and the development of the dunes. Indeed, linkage between turbulent structure and interaction with the water surface is theorised as the mechanism that limits dune height and thus plays a significant role in bedform phase control. Furthermore, as dunes are the principal element of resistance to flow in many channels they have a fundamental control on stage-discharge relationships and hence flooding levels for a given flow magnitude. Thus, an improved knowledge of these feedback processes is vital if we are better to model and manage many natural waterways and better predict how and where they both transport and deposit sediment. Whilst recent years have seen many advances in some aspects of mathematical modelling of macroturbulence generated by dunes, and have begun to elucidate some aspects of its shape and structure, this has not been matched by sufficient progress in measuring and quantifying such turbulence. This project proposes to use a combined laboratory investigation and numerical modelling approach to determine the topology and kinematics of large scale turbulence generated by dune bedforms. State-of-the-art laboratory technology, in the form of Particle Image Veocimetry, Laser Induced Fluorescence and High-Resolution Thermal Imaging, will enable us to quantify flows over fixed dune forms for a range of flow conditions. The results will allow us to answer important questions concerning the generation, form and dynamics of dune related turbulent structure, investigate how this is advected and interacts with the water surface and will also provide a benchmark dataset for improvements in numerical modelling codes. Such objectives are particularly needed in the future management of river channels, particularly in assessment flow resistance for flooding calculations, determination of sediment transport capacity and linking to an improved understanding of larger scale channel morphodynamics.

所有河流都沿着床并悬浮在水柱中，沿床的材料通常被水雕刻成各种形式：这些形式中最常见的一种是沙丘，这些沙丘在沙质和砾石沉积物中都可能产生。这样的沙丘几乎总是存在于冲积通道中，并且是通过流量运输更粗的沉积物的主要方式之一。世界上许多小河流都有这样的沙丘，在大河中，它们的长度可能高达600万，甚至数十个甚至数百米。这样的沙丘是由湍流产生的，但是一旦形成，就开始大大破坏它们在它们上移动的流动，从而从它们提供给水的电阻中的流量中提取能量，并在流动中产生大规模的湍流涡流或“大规模的湍流”。这些大规模的涡流经常被视为河流水面上的上升或“沸腾”的液体，对独木舟和船夫很熟悉。这种湍流本身可能负责悬挂和运输大量的沉积物，并成为流体流动，沉积物运动和沙丘发展之间一系列复杂的“反馈”过程的一部分。实际上，湍流结构与与水面的相互作用之间的连锁是理论上是限制沙丘高度，因此在床形相控制中起重要作用的机制。此外，由于沙丘是许多通道中耐药性的主要元素，因此他们对阶段解散关系具有基本的控制，因此在给定的流量幅度上泛滥。因此，如果我们更好地建模和管理许多天然水道，并更好地预测它们如何运输和沉积沉积物，那么对这些反馈过程的改进知识至关重要。尽管近年来在沙丘产生的大型扰动的数学建模的某些方面有了许多进步，并且已经开始阐明其形状和结构的某些方面，但在衡量和量化此类湍流方面的足够进展并不匹配。该项目建议使用合并的实验室研究和数值建模方法来确定沙丘床形成产生的大规模湍流的拓扑和运动学。最先进的实验室技术，以粒子图像的形式，激光诱导的荧光和高分辨率热成像，将使我们能够在一系列流动条件下量化固定沙丘形式的流量。结果将使我们能够回答有关与沙丘相关的湍流结构的生成，形式和动态的重要问题，研究如何推进并与水面相互作用，还将提供一个基准数据集，以改善数值建模代码。在未来对河道的管理中，尤其需要进行此类目标，尤其是在评估流量计算，确定沉积物运输能力以及与对大规模通道形态动力学的增强理解相关联时所需的目标。