High resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport

湍流引起的泥沙侵蚀和近河床移动的分析对水利工程的许多方面都至关重要，包括稳定通道的设计，桥墩的保护，水生栖息地的开发和管理，等等。目前可用于预测泥沙侵蚀阈值和河床输沙率的大多数关系都是经验性的，并采用时间和空间平均体积。因此，这些公式的预测能力很低，误差可能超过100%，这反映了对所涉及的物理机制缺乏充分的理解。拟议的研究将利用最先进的物理实验和通过球形和自然形状粗糙度元素的流动的数值模拟来解决这一知识差距。关键的研究目标包括识别和量化瞬时流场（包括粗糙度顶部以下的区域）与泥沙颗粒所产生的力之间的关系，评估单个床载颗粒轨迹以及湍流和众多移动泥沙颗粒的相互作用。其中，雷诺数、水流淹没度、沉积物形状和沉积物堆积对湍流结构和近床输运的影响将得到解决。这项研究将首次基于系统地使用高分辨率的数值模拟，其中包括完全分解的移动粗糙度元素，以及移动沉积层上下的先进三维实验测量。该项目将汇集来自两个国家的三个研究小组，它们在解决共同的研究目标方面具有独特的能力，相互补充。

Analysis of turbulence-induced sediment erosion and near-bed transport is vital to many aspects of hydraulic engineering including the design of stable channels, protection of bridge piers, and the development and management of aquatic habitats, to mention a few. Most currently available relationships for predicting sediment erosion thresholds and bed-load transport rates are empirical and employ time- and space-averaged bulk quantities. The predictive power of these formulae is therefore low and errors may well exceed 100 %, which is a reflection of the lack of sound understanding of the physical mechanisms involved. The proposed study will address this knowledge gap using state-of-the-art physical experiments and numerical simulations of flows over spherical and naturally shaped roughness elements. Key research targets include identification and quantification of relationships between instantaneous flow fields (including the region below roughness tops) and resulting forces on sediment particles, assessment of individual bed-load particle trajectories and the interaction of turbulent flow and a multitude of mobile sediment particles. Among others, the effect of Reynolds number, flow submergence, sediment shape, and sediment packing on turbulence structure and near-bed transport will be addressed. The study will be based, for the first time, on the systematic use of highly-resolved numerical simulations with fully resolved mobile roughness elements coupled with advanced three-dimensional experimental measurements above and below mobile sediment beds. The project will bring together three research groups from two countries which complement each other with unique capabilities in addressing a common research goal.