Cohesive Sediment Dynamics in Turbulent Flow

粘性沉积物是指尺寸小于约63微米的颗粒。 它存在于生态敏感的环境中，如河流，湖泊，河口和渔业。在这些环境中的污染物和营养盐输运的可靠预测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式。 对于粘性沉积物中的小颗粒，由于电荷引起的颗粒之间的吸引力常常主导水动力和重力。虽然这些吸引力可以导致颗粒形成更大的聚集体或“絮凝物”，但是湍流流体应力倾向于使絮凝物破碎。因此，粘性沉积物絮凝体的尺寸分布是由颗粒间和湍流应力的微妙平衡决定的，这会影响它们的传输速率。 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迁移过程。这项研究将通过一系列计算机模型和模拟来探索湍流环境中的粘性沉积物动力学。 其目的是开发可靠的预测工具，用于环境中营养物质和污染物的运输。 研究结果还将改善与其他技术相关的预测，包括深海碳氢化合物勘探。该研究将教育和培训一名博士生，以及本科生和高中生，在计算建模，流体动力学，泥沙输运和高性能计算。拟议的研究通过一系列日益复杂的计算调查，探索粘性泥沙在湍流环境中的动力学，基于从单向耦合，降阶拉格朗日点粒子模型到完全“四通”耦合的颗粒分辨直接数值模拟。它将解决一系列根本性的重要问题，其中包括：a）湍流特性如何影响沉积物絮凝/聚结和破碎之间的平衡？B）絮凝物的尺寸分布如何作为湍流和沉积物特性的函数而变化？粘性泥沙的有效沉速如何取决于紊流和泥沙特性？d）沉积物如何改变湍流特性？e）粘性泥沙对湍流的影响与非粘性泥沙有何不同？以及f）粘聚力如何影响沉积物床的可蚀性？设想的计算模拟将作为基础，制定比例尺的法律，捕捉动态的粘性泥沙在湍流中，这是适合于实施到现有的大规模泥沙输运models.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

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.