Cohesive Sediment Dynamics in Turbulent Flow

粘性沉积物指的是尺寸小于约63微米的颗粒。它存在于生态敏感的环境中，如河流、湖泊、河口和渔场。要想在这些环境中可靠地预测污染物和营养物的迁移，就需要精确的粘性沉积物动力学模型。我们目前缺乏这样的模型。对于粘性沉积物中的小颗粒，由于电荷而产生的颗粒之间的吸引力往往主导着水动力和重力。虽然这些吸引力可以使颗粒形成更大的聚集体或“絮凝体”，但湍流应力往往会破坏絮凝体。因此，粘性沉积物絮凝体的大小分布是由颗粒间应力和湍流应力的微妙平衡控制的，这影响了它们的运输速率。颗粒之间的吸引力也强烈影响海底沉积物的可蚀性，从而影响河流和海洋中的沉积物运输过程。本研究将通过一系列计算机模型和模拟来探索湍流环境中粘性沉积物动力学。其目的是为环境中营养物质和污染物的运输开发可靠的预测工具。该结果还将改进与其他技术相关的预测，包括深海油气勘探。该研究将在计算建模、流体动力学、泥沙输送和高性能计算方面教育和培训一名博士生、本科生和高中生。该研究通过一系列日益复杂的计算研究，探索了湍流环境中粘性沉积物的动力学，这些研究基于从单向耦合、降阶拉格朗日点粒子模型到完全“四向”耦合的颗粒解析直接数值模拟（DNS）等一系列方法。它将解决一系列非常重要的问题，其中包括：a)湍流特性如何影响沉积物絮凝/聚并和破碎之间的平衡？b)作为湍流和泥沙性质的函数，絮体大小分布如何变化？c)粘性泥沙的有效沉降速度如何取决于湍流和泥沙性质？d)泥沙如何改变湍流特性？e)粘性泥沙对湍流的影响与非粘性泥沙有何不同？f)黏结力如何影响沉积层的可蚀性？设想的计算模拟将作为制定尺度定律的基础，这些尺度定律可以捕捉湍流中粘性沉积物的动力学，并且适用于现有的更大规模的沉积物输运模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Cohesive sediment refers to particles below approximately 63 microns in size. It is present in ecologically sensitive environments such as rivers, lakes, estuaries, and fisheries. Reliable prediction of contaminant and nutrient transport in these environments requires accurate models of cohesive sediment dynamics. We currently lack such models. For the small particles in cohesive sediments, attractive forces between particles due to electric charges frequently dominate hydrodynamic and gravitational forces. While these attractive forces can cause the particles to form larger aggregates or "flocs", turbulent fluid stresses tend to break up the flocs. Hence, the size distribution of cohesive sediment flocs is governed by a delicate balance of interparticle and turbulent stresses, which affects their transport rates. The attractive forces between particles also strongly affect the erodibility of sediment deposits on the seafloor, which influences sediment transport processes in rivers and oceans. This research will explore cohesive sediment dynamics in turbulent environments via a series of computer models and simulations. The aim is to develop reliable, predictive tools for the transport of nutrients and contaminants in the environment. The results will also improve predictions related to other technologies, including deep sea hydrocarbon exploration. The research will educate and train a doctoral student, as well as undergraduate and high school students, in computational modeling, fluid dynamics, sediment transport, and high-performance computing.The proposed research explores the dynamics of cohesive sediment in turbulent environments via a series of increasingly complex computational investigations, based on a hierarchy of approaches ranging from one-way coupled, reduced-order Lagrangian point particle models to grain-resolving direct numerical simulations (DNS) that are fully `four-way' coupled. It will address a broad range of fundamentally important questions, among them: a) how do the turbulence properties affect the equilibrium balance between sediment flocculation/coalescence and break-up?, b) how does the floc size distribution vary as a function of the turbulence and sediment properties?, c) how does the effective settling velocity of the cohesive sediment depend on the turbulence and sediment properties?, d) how are the turbulence properties altered by the sediment?, e) how is the effect of cohesive sediment on turbulence different from that of non-cohesive sediment?, and f) how is the erodibility of a sediment bed affected by cohesive forces? The envisioned computational simulations will serve as basis for formulating scaling laws that capture the dynamics of cohesive sediment in turbulence, and which are suitable for implementation into existing larger-scale sediment transport models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.