High Resolution, Non-intrusive Shear Stress Measurement in Fluvial Environments

在许多情况下，包括砾石河床河流、漫流和部分充满的管道中，水流都是湍流。一个关键问题是这种湍流对构成许多天然河道边界的沉积物颗粒施加的动量和力。目前，一个空间平均的参数，称为剪切，是用来描述的动量/力，是从湍流传输到沉积物存款。流体和床之间的动量交换是一个关键的物理过程-能够理解这些过程将有助于理解沉积物和污染物如何移动，以及流动如何失去能量，从而确定流动深度。大多数河床是由多孔的、空间复杂的、三维的颗粒沉积物组成的，因此动量的空间和时间分布将控制水流和河床之间的污染物交换以及单个沉积物颗粒是否移动。目前，环境科学家只能以非常粗糙的方式测量边界剪应力，这些方法只能提供时间和空间平均测量值，其中许多依赖于在局部尺度上无法确定的经验参数。该项目提出开发一种系统，该系统能够在颗粒尺度上测量水流中的边界剪切应力，并且能够确定由观察到的湍流结构引起的边界剪切应力的波动。该系统使用了最初由航空工程师使用的概念。该项目团队将使用新的化学物质来制造能够附着在自然沉积物上的薄涂层，从而可以直接测量剪切应力。新的涂层将包含手性液晶（CLC），它会随着剪切应力的变化而改变颜色。使用薄膜涂层，结合适当的照明和图像捕捉技术，将意味着它是可能的，第一次，时间和空间波动力的颗粒在水工作的砾石床受到湍流的深度有限的流量。

Flows found in many situations, including gravel bed rivers, overland flows, and in partially filled pipes, are turbulent. A key issue is the momentum and forces that this turbulent flow imparts on the sediment grains that make up the boundaries of many natural channels. Currently a spatially averaged parameter, termed shear, is used to describe the momentum/force that is transmitted from the turbulent flow into the sediment deposit. The exchange of momentum between the fluid and bed is a key physical process - being able to understand the processes will help understanding of how sediments and pollutants move, and how flows lose energy and so determine flow depths. Most river beds are composed of porous, spatially complex, three-dimensional granular deposits so the spatial and temporal distribution of momentum will control the exchange of pollutants between the flow and the bed and whether individual sediment grains will move. Currently environmental scientists can only measure boundary shear stress in very crude ways, which only provide time and space averaged measurements, many of which rely on empirical parameters that are impossible to determine at a local scale. This project proposes to develop a system that would be able to measure boundary shear stress in a water flow at a grain scale and at a frequency capable of determining the fluctuations in boundary shear stress caused by observed turbulent flow structures. The system uses a concept originally used by aeronautical engineers. The project team will use novel chemistry to create thin coatings capable of being attached to natural sediments that can measure shear stress directly. The new coatings will contain chiral nematic liquid crystals (CLCs), which change colour in response to changes in shear stress. The use of thin film coatings, combined with suitable illumination and image capture techniques, will mean that it is possible to measure, for the first time, the temporal and spatial fluctuating forces on grains in water-worked gravel beds subjected to turbulent depth-limited flows.