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研究沉积物悬架和运输研究的历史悠久，这是由于河流的冲刷过程的重要性。 对于河流和风吹雪或雪，悬架过程由边界上的流体流动引起的湍流控制，即床上的流动。 然而，悬浮的流量通常会受到从边界产生的湍流，这种类型的沉积物悬架过程很少进行研究。在环境和工业流中广泛发现了例子。考虑一下swash区的具体例子，swash区是海滩的区域，该区域被波浪升起和沿海侵蚀的主要位置交替覆盖和揭开。 在向上的波浪期间，湍流水平由破裂波和孔塌陷产生的湍流主导，而边界生成的湍流相对较小。实验室研究的一个很大优势是能够将不同的物理过程与更复杂的多物理现实隔离开来。 建议使用在先前的NSF项目上开发的独特湍流设施进行基本的实验研究计划，该设施通过随机触发以八×八八八键的网格组装而产生的湍流来产生湍流。 这些喷气机会产生强大的湍流，平均流量很小。湍流从阵列和沙子床传播，在那里悬架仅由于湍流而发生。这纯粹是通过湍流纯粹研究沉积物悬浮液的仔细研究。 定量成像（QI）技术将用于表征湍流的细节以及导致悬浮和波纹形成的沉积物谷物运动的细节。 QI测量值将用于确定负责沉积物悬浮液的瞬时湍流结构，并专门研究流体在沉积物运动中的作用以及沉积物对流体运动的作用。 将构建湍流应力的一体平均图片，在时空中构建，从而开发适合将沉积物悬架过程的参数化，适合包含在沉积物悬架和运输的计算模型中。对地方经济至关重要，具有战略重要性。调查显示，近90％的美国沙海岸正在侵蚀 - 在东海岸，每年以1米的速度以1米的速度。 已经观察到了每米海岸线每秒至每秒10公斤的sw缝区沉积物传输速率的现场测量。这些明显高于在冲浪区域中较远的海面。升高的水平是由于边界生成的湍流，平均电流和强烈的环境湍流水平的复杂相互作用所致。 Swash区沉积物的传输仅代表着一系列重要的流动之一，其中湍流从边界占主导地位悬挂和动力学。 在没有平均流量的情况下，了解湍流悬浮液是一个关键的构件，可以在其上开发出更好的沉积物悬架模型。这些将显着提高我们建模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。对于一个对教师职业感兴趣的才华横溢的女性，他们将与PIS一起主持一项基于询问的项目，针对考虑科学和工程学职业的高中妇女的环境运输过程。