Development of a combined Lagrangian / Eulerian approach to understand coherent flow structures in gravel-bed rivers

河流中的沉积物运动是由流体力驱动的，它对河流地貌、生态和管理产生广泛的影响。传统上，水流和泥沙运动是在时间平均、连续的基础上进行分析和建模的，但众所周知，近床速度存在大的湍流波动，因此，在移动泥沙的阻力和升力中也存在大的湍流波动。砾石河床中的湍流不是一个简单的随机场：可视化和多点测量表明，可以将复杂的，多尺度的，准随机流场分解为基本的有组织结构，这些结构具有空间和时间相干性，称为漩涡或相干流结构。本研究的目的是发展一个增强的定量理解的产生，演变和消散的砾石河床的相干流结构。这将通过一系列概念验证实验室水槽实验来实现，这些实验室水槽实验在英国装备最好的环境流体动力学实验室中使用新型自动湍流映射技术。该技术给出了通过将示踪剂注入流动中揭示的相干流结构的欧拉和拉格朗日相结合的观点，这使得我们能够监测并从而理解运动学和物理学。（尺寸、尺度、形状、涡度和能量）和动力学特性（起源、稳定性、增长、当这些相干流结构产生并在复杂地形上移动时，包括砾石床表面。所提出的方法将使我们既增加我们的现象学的理解砾石河床河流的相干流结构和开发和改进的时间相关的数值模型的流量在这样复杂的表面。

Sediment movement in rivers, which has wide-ranging consequences for fluvial landforms, ecology & management, is driven by fluid forces. Flow & sediment movement has traditionally been analysed & modelled on a time-averaged, continuum basis, but it is well known that large turbulent fluctuations exist in near-bed velocity, & therefore in the drag & lift forces that move sediment. Turbulence in gravel-bed rivers is not a simple random field: visualisation & multipoint measurements show it is possible to decompose complex, multi-scaled, quasi-random flow fields into elementary organized structures which posses both spatial & temporal coherence that are called either eddies or coherent flow structures. The aim of this research is to develop an enhanced quantitative understanding of the generation, evolution & dissipation of Coherent Flow Structures in Gravel Bed Rivers. This will be achieved by a series of proof-of-concept laboratory flume experiments using novel automated turbulence mapping techniques in the UK's best-equipped environmental fluid dynamics laboratory. The techniques give a combined Eulerian and Lagrangian view of Coherent Flow Structures revealed by injecting tracers into the flow that allows us to monitor and thus understand both the kinematic (size, scaling, shape, vorticity & energy) & dynamic properties (origin, stability, growth, genesis into new forms & contribution to the time average flow) of these Coherent Flow Structures as they are prduced and move over complex topographies, including gravel bed surfaces. The proposed methodology will allow us to both increase our phenomenological understanding of Coherent Flow Structures in Gravel bed rivers & develop & improve time dependent numerical models of flow over such complex surfaces.