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.

PI：Christensen，Kenneth / Best，James / Anderson，Williamproposal编号：1603211 /1604155 /1603254拟议研究的重点是探索大规模，沙漠环境或海洋地板环境中沙丘的迁移。提出的协作方法涉及实验，理论和模拟，以了解湍流下的沙丘迁移过程。这项工作的发现对于风格的沙丘迁移可能很重要，这对于预测和缓解荒漠化至关重要的问题是在美国西部和世界其他地方的荒漠化。理解和预测巴chanbarchan dunes的形态动力学对于水道的管理和量化营养和污染者和污染者的运输至关重要。同样，了解风险肉沙丘的这些过程对于表征荒漠化过程和告知数字天气预测的重要性很重要。在大的沙丘间距下，可以使用基于平均床剪应力的沉积物传输模型来准确预测Barchan运动学。但是，Barchans通常发生在田野中。由于沙丘迁移率取决于尺寸，因此异质的沙丘场将导致可变的床形间距，而较小（更快）的沙丘接近较大（较慢）的沙丘。因此，当两个沙丘处于近距离状态时，上游将产生一个不稳定，湍流的唤醒，将雕刻下游的形态，从而引入显着的形态复杂性，这由于空间异质的湍流。当前的最新模型不会捕获此类效果。 （这些方法模拟了床形的演变，但不能解析上覆的流；而是将湍流的空间均匀表示作为流量输入）。在初步研究中得知，并被现有的沙丘建模方法中的缺陷所强迫，可以假设，阐明相互作用的Barchan Dunes的形态动力学的“缺失链接”是跨道恩间空间内产生的湍流的不稳定性质。有人建议从事协作研究工作，以利用创新的测量协议和科学计算，并得到自然观察的补充。结果将改变对固定床沙丘对固定床的沙丘流场相互作用的理解，这是邻近和体积比的函数，并将构成前进的形态动力学模型的基础。针对目标的沙丘配置，将在折射率匹配的环境（允许对流动的前所未有的光学访问）中进行平面和体积PIV测量。这些实验将验证大型模拟，这些模拟将使更大的空间体积和更广泛的沙丘野外参数探索，而后者通过现场观察得出。最终的任务将涉及将确定的湍流异质性纳入现有的形态动力学模型以检验假设。 拟议的工作不仅会影响流体动力学对工程湍流的影响，还将影响其他学科，包括边界层气象，地貌和沉积学。