Turbulent sediment suspension absent mean flow-induced shear

由于河流冲刷过程的重要性，泥沙悬浮和输移的研究有很长的历史。在河流和风沙或雪的情况下，悬浮过程由边界上的流体流动引起的湍流控制--也就是说，床面上的流动。然而，泥沙悬浮流往往受到远离边界产生的湍流的影响，这种类型的泥沙悬浮过程的研究很少。在环境和工业流动中，例子比比皆是。考虑冲浪区的具体例子，即被海浪抬高交替覆盖和未覆盖的海滩区域，以及海岸侵蚀的主要位置。在涌浪过程中，破碎波产生的湍流水平占主导地位，而边界产生的湍流水平相对较小。实验室研究的一大优势是能够将不同的物理过程从更复杂的多物理现实中分离出来。它被提议使用一种独特的湍流设备来进行基础实验研究计划，该设备是在之前的NSF项目基础上开发的，该设备通过随机发射一组以8乘8的网格组装的射流来产生湍流。这些喷流产生强烈的湍流，平均气流很少。湍流从阵列传播到沙床，在那里仅由于湍流而发生悬浮。这有利于仔细研究纯湍流作用下的泥沙悬浮物。定量成像(QI)技术将被用来描述导致悬浮和波纹形成的湍流和沉积物颗粒运动的细节。QI测量将被用来确定导致泥沙悬浮的瞬时湍流结构，并具体研究流体对泥沙运动的作用以及泥沙对流体运动的作用。将构建湍流应力在空间和时间上的集合平均图，从而开发适合于包括在泥沙悬浮和输运计算模型中的泥沙悬浮过程的参数化。美国沿海地区人口稠密，对当地经济至关重要，具有战略重要性。调查显示，近90%的美国沙质海岸正在以每年一米的速度侵蚀东海岸。观测到的冲浪区泥沙输移率高达每米海岸线10公斤/秒；这远远高于海浪区更远的海域观测到的输沙率。水平升高是由于边界产生的湍流、平均气流和伴随着波浪破碎过程平流的强烈环境湍流水平的复杂相互作用。冲刷带泥沙输送只是一系列重要水流中的一种，在这些水流中，远离边界产生的湍流主导着泥沙的悬浮和动力学。理解在没有平均流的情况下的湍流悬浮物是建立更好的泥沙悬浮物模型的关键。这些将大大提高我们模拟工业和环境侵蚀和沉积过程的能力。该项目将为一位对教职生涯感兴趣的有才华的女性带来一个博士学位，她将与PI一起，为考虑从事科学和工程职业的高中女性主持一个基于调查的项目，内容是环境交通流程。

1233842CowenThe study of sediment suspension and transport has a long history, due to the importance of scour processes in rivers. In the case of rivers and wind-blown sand or snow, the suspension processes are controlled by the turbulence induced by the fluid flow over the boundary - that is, the flow over the bed. However, sediment-suspending flows are often subject to turbulence that was generated away from the boundary, and this type of sediment suspension process has seen very little research. Examples are widely found in environmental and industrial flows. Consider the specific example of the swash zone, the region of the beach that is alternately covered and uncovered by wave run-up and the principal location of coastal erosion. During wave up-rush, turbulence levels are dominated by turbulence advected from breaking waves and generated by bore collapse, while boundary-generated turbulence is relatively small. A great advantage of laboratory research is the ability to isolate distinct physical processes from the more complex multi-physics reality. It is proposed to carry out a fundamental experimental research program using a unique turbulence facility, developed on a previous NSF project, which generates turbulence by randomly firing an array of jets assembled in an eight-by-eight grid. These jets generate strong turbulence, with very little mean flow. The turbulence propagates away from the array and towards a bed of sand, where suspension due solely to the turbulence occurs. This facilitates the careful study of sediment suspension purely by turbulence. Quantitative imaging (QI) techniques will be used to characterize the details of the turbulence and the sediment grain motions that lead to suspension and ripple formation. The QI measurements will be used to determine the instantaneous turbulence structures responsible for sediment suspension and to specifically investigate the role of both the fluid on the sediment motions and the sediment on the fluid motions. An ensemble mean picture of the turbulent stresses, in space and time, will be constructed, allowing the development of parameterizations of the sediment suspension process appropriate for inclusion in computational models of sediment suspension and transport.Coastal areas in the United States are heavily populated, vital to local economies, and of strategic importance. Surveys reveal that nearly 90% of U.S. sandy coasts are eroding - on the East Coast at rates on the order of one meter per year. Field measurements of swash zone sediment transport rates as large as 10 kilograms per second per meter of shoreline have been observed; these are significantly higher than those observed farther seawards in the surf zone. The elevated levels are due to a complex interaction of boundary-generated turbulence, mean currents, and strong ambient turbulence levels advected with the wave breaking processes. Swash zone sediment transport represents just one of a range of important flows in which turbulence generated away from the boundary dominates sediment suspension and dynamics. An understanding of turbulent suspension in the absence of mean flows is a critical building block on which better models of sediment suspension can be developed. These will significantly improve our ability to model industrial and environmental erosive and depositional processes. The project will lead to a Ph.D. for a talented woman interested in a faculty career who, along with the PIs, will host an inquiry-based project on environmental transport processes for high-school women considering careers in science and engineering.