CAREER: Interaction between Turbulence Structures and Suspended Sediment in Rivers

泥沙在悬浮体中的湍动输移对许多地质和环境问题具有重要意义。在大多数情况下，悬浮泥沙浓度会非常迅速地从泥沙床上移开。因此，预测悬浮泥沙通量的最重要因素是对非常接近泥沙床的悬浮泥沙进行准确的估计。有许多公式被引入来预测这种近床层浓度，但这些公式的估计值差别很大。目前尚无定性或定量的模型来描述水力湍动水流中悬浮泥沙颗粒夹带和脱离床面的实际过程。该奖项的主要目标之一是发展对悬浮泥沙夹带过程的理解，以及从具有同时推移质的水力粗糙床中剥离悬浮泥沙的过程。假设卷吸和脱卷过程不仅受具有正的垂直向上速度的近床湍流结构的控制，而且还受床面悬浮颗粒的可用性控制。可利用性可能受悬浮颗粒在床面的挖掘和埋藏控制。为了了解这一过程，将在实验室水槽中使用高速视频系统、激光光片和一套新颖的混合PIV-PTV算法进行一些定量可视化实验。通过计算非常多的推移质颗粒和悬浮颗粒的同时运动，对整个泥沙卷吸和脱沙过程进行了数值模拟。这些运动将由时间和空间上真实的湍流结构驱动。最后，悬沙输移场将与河道中出现的大尺度横向湍流结构相耦合。横向结构将在实验室流量表和河流中使用PIV-PTV测速技术进行研究。然后计算结构物对输沙场的修正作用。在研究生和本科生的帮助下，将建立一个学生地球表面流体实验室。该实验室将包括一个用于地下水流动调查的Hele-Shaw水槽，一个用于水流和河道变化调查的流量表，以及一个用于泥沙输送实验的泥沙循环水槽。此外，实验室还将配备工具和材料，为学生指导的项目建造其他小型实验设备。将为每个实验室设备编写一套流动结构解析数值例程。将开设一门地球表面流体实验课程。本课程将提供如何构建、设置和测量流动结构的实践经验。这门课的重点是开发学生指导的研究项目。我们将继续为研究生开设一门新开设的泥沙输运力学课程，并将结合这项拟议研究的结果。此外，还将继续为地质学本科生开发一门新的“影子课程”，在介绍微积分和物理的地质应用的同时，辅导学生的家庭作业。

The transport of sediment in suspension by turbulent flows is important to a large number of geologic and environmental problems. In most instances, the suspended sediment concentration decreases very rapidly moving away from the sediment bed. Therefore, the most important factor in predicting the suspended sediment flux is an accurate estimate of suspended sediment very near the sediment bed. Numerous formulas have been introduced to predict this near-bed concentration, but estimates from these formulas vary considerably. There exists no qualitative or quantitative model for the actual process by which suspended sediment grains are entrained and disentrained from the bed of a hydraulically rough flow. One of the primary goals of this award is to develop an understanding of the process of suspended sediment entrainment and disentrainment from a hydraulically rough bed with simultaneous bedload transport. It is hypothesized that the entrainment and disentrainment process is governed not only by near-bed turbulence structures with positive, vertically upward velocities, but also by the availability of suspended-size particles at the bed surface. The availability is presumably controlled by the exhumation and burial of suspended-size particles at the bed surface. To understand this process, a number of quantitative visualization experiments will be conducted in a laboratory flume using a high-speed video system, laser light sheet, and a suite of novel hybrid PIV-PTV algorithms. A numerical simulation of the overall entrainment and disentrainment will be performed by calculating the simultaneous motions of a very large number of bedload and suspended-size particles. The motions will be driven by temporally and spatially realistic turbulent structures. Finally, the suspended sediment transport field will be coupled to large-scale lateral turbulent structures occurring in river channels. The lateral structures will be investigated in a laboratory stream table and in a river using PIV-PTV velocimetry techniques. Then the modification of the sediment transport field by the structures will be calculated. A Student Earth Surface Fluid Laboratory will be built with the help of graduate and undergraduate students. The laboratory will consist of a hele-shaw cell for ground-water flow investigations, a stream table for flow and channel change investigations, and a sediment recirculating flume for sediment transport experiments. Also, the lab will be equipped with tools and materials to build other small experimental devices for student directed projects. A set of flow-structure-resolving numerical routines will be written for each of the laboratory devices. A course in earth surface fluid experiments will be developed. The course will provide hands-on experience of how to build, setup, and take measurements of flow structures. The focus of the class will be on developing student directed research projects. A newly introduced sediment transport mechanics course for graduate students will continue to be developed with material incorporated from results of this proposed research. Also, a new "shadow course" for geology undergraduates will continue to be developed that tutors students with their homework while introducing geologic applications of calculus and physics.