Collaborative Research: Coordinated Experiments and Simulations of Near-Surface Turbulent Flow over Barchan Dunes: Informing Models of Dune Migration and Interaction

合作研究：新月形沙丘近地表湍流的协调实验和模拟：为沙丘迁移和相互作用模型提供信息

• 批准号: 1603211
• 负责人: Kenneth Christensen
• 金额: $ 26.82万
• 依托单位: University of Notre Dame
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1603211&HistoricalAwards=false
• 关键词: Collaborative; Research; Coordinated; Experiments; Simulations

PI: Christensen, Kenneth / Best, James / Anderson, WilliamProposal Number: 1603211 / 1604155 / 1603254The focus of the proposed research is to explore the migration of sand dunes in large scale, desert environments or ocean floor environments. The proposed collaborative approach involves experiments, theory and simulations to understand the process of dune migration under turbulent flow. The findings of this work can be important for Aeolian dune migration, a problem that can be critical to predicting and mitigating desertification as it occurs in the Western US and in other places in the world.Understanding and predicting the morphodynamics of subaqueous barchan dunes is critical for management of waterways and quantifying transport of nutrients and pollutants. Similarly, understanding these processes for aeolian barchan dunes is important for characterizing desertification processes and for informing numerical weather prediction. At large dune spacings, barchan kinematics can be accurately predicted using sediment transport models predicated on mean bed shear stress. However, barchans typically occur in fields. Since dune migration rate is size dependent, a heterogeneous dune field will result in variable bedform spacing, with smaller (faster) dunes approaching larger (slower) dunes. Thus, when two dunes are in close proximity, the upstream one will produce an unsteady, turbulent wake that will sculpt the morphology of the downstream one, introducing significant morphological complexity owing to spatially-heterogeneous turbulence. Such effects are not captured by current state-of-the-art models. (These approaches simulate the bedform evolution but do not resolve the overlying flow; they instead use a spatially homogeneous representation of turbulence as the flow input). Informed by preliminary research, and compelled by deficiencies in existing dune modeling approaches, it is hypothesized that the "missing link" to elucidating the morphodynamics of interacting barchan dunes is the unsteady nature of the turbulence generated within the inter-dune space. It is proposed to pursue a collaborative research effort that leverages an innovative measurement protocol and scientific computing, complemented by observations in nature. The results will transform the understanding of dune-dune flow field interactions for fixed-bed dunes as a function of proximity and volumetric ratio and will form the basis for advancing morphodynamic models. Planar and volumetric PIV measurements will be conducted in a refractive-index-matched environment (allowing unprecedented optical access to the flow) for targeted dune configurations. These experiments will validate large-eddy simulations that will enable larger spatial volumes and a much broader suite of dune field parameters to be explored, with the latter informed by field observations. The culminating task will involve incorporating the turbulence heterogeneity identified into existing morphodynamic models to test the hypothesis. The proposed work will have an impact not only in fluid dynamics through its impact on engineering turbulent flows, but also to other disciplines including boundary-layer meteorology, geomorphology and sedimentology.

主要研究者：Christensen，Kenneth / Best，James /安德森，William建议编号：1603211 / 1604155 /1603254建议研究的重点是探索沙丘在大尺度、沙漠环境或海底环境中的迁移。所提出的合作方法涉及实验，理论和模拟，以了解湍流下沙丘迁移的过程。这项工作的结果可能是重要的风成沙丘迁移，一个问题，可以是至关重要的预测和减轻荒漠化，因为它发生在美国西部和世界其他地方。了解和预测水下新月形沙丘的形态动力学是至关重要的水道管理和量化运输的营养物质和污染物。同样，了解风成新月形沙丘的这些过程对于描述荒漠化过程和提供数值天气预报信息也很重要。在大沙丘间距，新月形沙丘运动学可以准确地预测使用平均床面剪切应力预测的泥沙输运模型。然而，barchans通常发生在领域。由于沙丘迁移速率取决于沙丘的大小，异质沙丘场将导致可变的底形间距，较小（较快）沙丘接近较大（较慢）沙丘。因此，当两个沙丘非常接近时，上游沙丘将产生不稳定的湍流尾流，该尾流将塑造下游沙丘的形态，由于空间不均匀的湍流而引入显著的形态复杂性。目前最先进的模型没有捕捉到这种影响。（这些方法模拟底形演变，但不解决上覆流;它们使用湍流的空间均匀表示作为流输入）。通过初步研究，并被迫在现有的沙丘建模方法的不足之处，它是假设的“缺失环节”，以阐明相互作用新月形沙丘的形态动力学是沙丘间空间内产生的湍流的非定常性质。建议开展合作研究工作，利用创新的测量协议和科学计算，并辅之以自然观测。研究结果将改变对固定床沙丘沙丘流场相互作用的理解，作为邻近度和体积比的函数，并将形成推进形态动力学模型的基础。平面和体积PIV测量将在折射率匹配的环境中进行（允许前所未有的光学访问流）的目标沙丘配置。这些实验将验证大涡模拟，这将使更大的空间体积和更广泛的一套沙丘场参数进行探索，后者通过实地观察。最终的任务将包括将湍流异质性识别到现有的形态动力学模型，以测试的假设。 拟议的工作不仅将通过其对工程湍流的影响而对流体动力学产生影响，而且还将对包括边界层气象学、地貌学和沉积学在内的其他学科产生影响。