Collaborative Research: Role of Turbulence Structure in Bedload Transport

足够快的流体流过可侵蚀的沙子和砾石床，携带表面颗粒，然后这些颗粒作为推移质滚动和跳跃。该项目旨在建立流体流动和推移质输运之间的定量预测关系，以便更准确地包含由于湍流而引起的流速波动的作用，而湍流总是存在。这种关系将适用于河流和波浪下普遍存在的非均匀或非稳定流，并将为从涟漪和沙丘到沙坝和河道再到分类和分级的侵蚀和沉积沉积特征的形成提供新的见解。该项目将研究(1)简单床型(如垫层和低沙丘)上的湍流结构和推移质输运，(2)床面粗糙度沿河流突然变化的湍流结构，(3)固定天然床面颗粒上的湍流结构和脉动力，(4)卷吸过程中作用在推移质颗粒上的湍流结构和流体力，以及(5)移动推移质颗粒对水流速度和湍流结构的影响。此外，该项目将通过以下方式进一步发展我们的离散颗粒计算模型：(1)更好地处理床面和推移质颗粒上的升力以及颗粒加速时流体上的反作用力；(2)将其与现有的三维床面湍流数值模拟相结合。这项拟议的研究涉及三个相互交织的问题：作用在床上并在床上移动的颗粒所受的力如何与近床流体速度的时间和空间分布有关，这些颗粒的卷吸和运动如何与这些力有关，以及移动的推移质的存在如何改变近床流体的速度。

Sufficiently fast fluid flows over erodible beds of sand and gravel entrain surface particles, which then roll and hop along as bedload. This project aims to develop quantitative predictive relations between fluid flow and bedload transport that more precisely incorporate the role of the fluctuating flow velocities due to turbulence, which always is present. Such relations will apply to the non-uniform or unsteady flows that are ubiquitous in streams and beneath waves and will provide new insight into the formation of erosional and depositional sedimentary features from ripples and dunes to bars and channels to sorting and grading. The project will investigate (1) turbulence structure and bedload transport over simple bedforms such as bedload sheets and low dunes, (2) turbulence structure over abrupt streamwise changes in bed roughness, (3) turbulence structure and the fluctuating forces on fixed natural bed particles, (4) turbulence structure and the fluid forces that act on bedload particles during entrainment, and (5) the modification of fluid velocity and turbulence structure by moving bedload particles. In addition, the project will further develop our discrete-particle computational model for sediment transport by (1) incorporating into it better treatment of the lift forces on bed and bedload particles and of the reaction forces on the fluid as the particles accelerate and (2) coupling it with an existing numerical simulation of turbulent flow over three-dimensional bedforms. The proposed research addresses three intertwined issues: how the forces exerted on particles on the bed and moving over it are related to the temporal and spatial distribution of the near-bed fluid velocities, how the entrainment and motion of those particles are related to the forces, and how the near-bed fluid velocities are modified by the presence of the moving bedload.