The Role of Relative Submergence on Flow-Obstacle Interaction: Implications to Sediment Transport

1033732 buchholz床上安装的障碍物，或离散的粗糙度元件延伸到流动的流体中，在广泛的自然和工程系统中无处不在。这种简单的几何形状创造了一个非常复杂的三维非定常流场，可以显著增加河床剪切应力和传热，并影响河流环境中的沉积物通量。虽然很明显，在广泛的参数范围内，主要的流动模式在质量上是相当强大的，但关于这些结构的动力学，围绕身体的床应力的最终分布，以及控制这些应力的湍流输送机制，特别是在浅层流动中，仍然有很多没有得到很好的理解。在陡峭的山涧中，天然障碍物或巨石的长度尺度与水流深度和河流宽度相当，这就引入了一个新的主要参数：相对淹没度H/D（其中H为水流深度，D为障碍物特征维数）。这些自然形成的障碍物通常具有H/D1，在这些条件下，沉积物沉积模式与大H/D时明显不同。这项工作旨在描述相对淹没对床上剪切应力分布的影响，以及障碍物周围的平均流量和沉积物沉积模式，并阐明控制这些过程的物理机制。这些目标将在浅明渠流中粗糙床上的球形障碍物的参数化研究中实现。粒子图像测速将用于获得速度和涡度场的定量测量，以及障碍物周围的湍流应力。流动的谱分析和条件平均将有助于阐明造成所观察到的应力的流体动力学机制。在相同的水流条件下，障碍物周围的泥沙淤积模式和相应的泥沙捕集效率将被表征。流动和沉积物研究将结合起来，提供河床剪切应力的总体测量，可用于预测涉及大型障碍物的更复杂河流环境中的沉积物运输特征。智力价值：这项调查涉及到一个高度相关的参数空间区域，迄今为止很少受到关注，并将为控制河流系统中沉积物运输的最近观察的物理机制提供基本见解。因此，这将导致一系列新的强大工具，以更有效地管理国家的河流。从根本上说，这项工作将为流动结构动力学、湍流应力和障碍物附近的沉积物运动之间的复杂相互作用提供更清晰的画面，这可能具有远远超出本工作所基于的原型问题类别的含义。尽管对障碍物周围流动的研究已经进行了几十年，但由于研究人员在流体动力学和泥沙输运方面的整合，以及使用了先进的测量方法，这项工作具有很大的潜力。更广泛的影响：由于流动在壁挂式障碍物上的无处不在，这项工作的技术影响有可能影响河流管理、空气动力学、城市规划、工业厂房设计、传热等领域的广泛应用。该项目还为研究环境水力学和流体动力学的研究生和本科生提供了宝贵的多学科教育机会，因此为培养下一代科学家提供了理想的环境。学校和社区学院的社区外展活动将支持“基于科学的河流修复方法”这一主题。

1033732BuchholzBed-mounted obstacles, or discrete roughness elements extending into a flowing fluid, are ubiquitous in a broad range of natural and engineered systems. This simple geometry creates a very complex, three-dimensional and unsteady flow field that can significantly increase bed shear stresses and heat transfer, and affect sediment fluxes in fluvial environments. While it is apparent that the dominant flow patterns are qualitatively quite robust under a broad range of parameters, there is still much that is not well understood about the dynamics of these structures, the resulting distribution of bed stresses surrounding the body, and the turbulent transport mechanisms that govern these stresses, especially in shallow flows. In steep mountain streams, naturally-occurring obstacles or boulders are of comparable length scale with flow depth and river width, which introduces a new and primary parameter: the relative submergence H/D (where H is the flow depth and D is the obstacle characteristic dimension). These naturally-occurring obstacles typically have H/D1, and under these conditions the sediment depositional patterns are strikingly different than at large H/D. This work seeks to characterize the effects of relative submergence on bed shear stress distributions, and mean flow and sediment depositional patterns surrounding the obstacle, and to elucidate the physical mechanisms governing these processes. These objectives will be achieved in a parametric study of a spherical obstacle on a rough bed in shallow open-channel flow. Particle image velocimetry will be used to obtain quantitative measurements of the velocity and vorticity fields, and turbulent stresses surrounding the obstacle. Spectral analysis and conditional averaging of the flow will help to elucidate the fluid-dynamic mechanisms responsible for the observed stresses. For the same flow conditions, sediment deposition patterns around the obstacle and corresponding sediment trapping efficiencies will be characterized. The flow and sediment studies will be combined to provide insight on aggregate measures of bed shear stress that can be used to predict sediment transport characteristics in more complex riverine environments involving large obstacles.Intellectual Merit: This investigation addresses a highly relevant region of the parameter space which has so far received little attention, and will provide fundamental insights into the physical mechanisms governing recent observations about sediment transport in fluvial systems. Therefore, this will lead to a new array of powerful tools to more effectively manage the nation's rivers. Fundamentally, the work will provide a clearer picture of the complex interactions between flow structure dynamics, turbulent stresses, and sediment movement in the vicinity of an obstacle, which can have implications far beyond the prototype class of problems on which this work is based. Despite many decades of research on flow around obstacles, the proposed work has great potential due to the integration of researchers in fluid dynamics and sediment transport, and the use of advanced measurement methods.Broader Impacts: Due to the ubiquity of flow over wall-mounted obstacles, the technical impacts of this work have the potential to affect a wide range of applications in the areas of river management, aerodynamics, urban planning, industrial plant design, heat transfer, and many others. The project also provides an invaluable multi-disciplinary educational opportunity for graduate and undergraduate students studying environmental hydraulics and fluid dynamics, and therefore provides an ideal environment for the training of the next generation of scientists. Community outreach in schools and community colleges will support the theme "Science Based Restoration Approaches for Rivers".