Turbulent sediment suspension absent mean flow-induced shear

湍流沉积物悬浮液不存在平均流引起的剪切

• 批准号: 1233842
• 负责人: Edwin Cowen
• 金额: $ 30万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1233842&HistoricalAwards=false
• 关键词: Turbulent; sediment; suspension; absent; mean

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.

1233842考恩由于河流冲刷过程的重要性，泥沙悬浮和输移的研究有着悠久的历史。 在河流和风吹沙或雪的情况下，悬浮过程由边界上的流体流动（即床上的流动）引起的湍流控制。 然而，悬沙水流往往受到远离边界产生的湍流的影响，这类悬沙过程的研究很少。在环境和工业流动中广泛存在这方面的例子。考虑冲流区的具体例子，该区域的海滩交替地被波浪爬高覆盖和暴露，并且是海岸侵蚀的主要位置。 在波浪涌升过程中，湍流水平主要由破碎波平流和涌浪溃灭产生的湍流控制，而边界产生的湍流相对较小。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场现实中分离出来。 建议使用一种独特的湍流设施进行基础实验研究计划，该设施是在以前的NSF项目上开发的，它通过随机发射一组组装在8 × 8网格中的射流来产生湍流。 这些射流产生强烈的湍流，平均流量很小。湍流远离阵列并朝向沙床传播，在沙床处仅由于湍流而发生悬浮。这有助于对纯粹由湍流引起的泥沙悬浮进行仔细研究。 定量成像技术将用于描述湍流和沉积物颗粒运动的细节，这些运动导致悬浮和涟漪的形成。QI测量将用于确定造成沉积物悬浮的瞬时湍流结构，并专门研究流体对沉积物运动和沉积物对流体运动的作用。 一个合奏平均图片的湍流应力，在空间和时间，将被构建，允许参数化的沉积物悬浮过程的发展适合列入计算模型的沉积物悬浮和transport.Coastal地区在美国人口稠密，对当地经济至关重要，具有战略意义。调查显示，近90%的美国桑迪海岸正在侵蚀--在东海岸，侵蚀速度约为每年一米。 已观察到冲刷区沉积物输运速率高达每秒每米海岸线10公斤的实地测量结果;这些结果明显高于在碎浪区更远的海域观察到的结果。升高的水平是由于边界产生的湍流，平均电流，和强烈的环境湍流水平平流与波浪破碎过程的复杂的相互作用。冲浪区泥沙输运只是一系列重要流动中的一种，在这些流动中，远离边界产生的湍流支配着泥沙悬浮和动力学。 在没有平均流的情况下理解湍流悬浮是一个关键的基石，在此基础上可以开发更好的沉积物悬浮模型。这将大大提高我们模拟工业和环境侵蚀和沉积过程的能力。该项目将导致博士学位。对于一个有才华的女人感兴趣的教师职业生涯谁，沿着的PI，将主办一个基于调查的项目环境运输过程的高中妇女考虑在科学和工程的职业生涯。