Collaborative Res: Physics of lutoclines and laminarization extracted from turbulence-resolved numerical investigations on sediment transport in wave-current bottom boundary layer

协作研究：从波流底部边界层沉积物输运的湍流解析数值研究中提取的卢斜层和层化物理

• 批准号: 1131016
• 负责人: Sivaramakrishna Balachandar
• 金额: $ 26.67万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-15 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1131016&HistoricalAwards=false
• 关键词: Collaborative; Res; Physics; lutoclines; laminarization

Recent numerical investigations reveal the existence of four distinct regimes of wave-induced fine sediment transport ranging from well-mixed transport, to the formation of a lutocline, and eventually a complete flow laminarization over a range of sediment availabilities and settling velocities. The numerical model is based on an Eulerian-Eulerian two-phase formulation simplified for fine sediment (small particle response time) while resolving all the scales of turbulence-sediment interactions. This project will further investigate four critical science issues related to these regimes via numerical simulations. Firstly, a complete phase map will be constructed of flow regimes as a function of wave Reynolds number, bulk Richardson number (sediment availability) and nondimensional settling velocity with a series of carefully designed simulations. The results will highlight the major differences between the tidal and wave boundary layers in response to sediments. Secondly, with a better understanding of the onset of laminarization, the model will be enhanced to support non-Newtonian rheology in order to study the interplay between rheological stress and turbulence modulation in determining the transition of flow regimes and hydrodynamic dissipation. Thirdly, mean current will be added to the simulations. Wave-current interaction may enhance the mud layer thickness and transport, as observed in a recent field study at the shelf of Waiapu River (New Zealand). However, if the current is too strong, sediments can be re-entrained and become well-mixed and hence the formation of gravity flow is prevented. Finally, the model will be expanded for transport of coarser grains. Concurrent transport of clay and silt due to decreasing wave Reynolds number will be first studied. Next step will be to simulate a complete polydispersed system using a direct quadrature method of moments approach. Polydispersed simulation efforts allow insights into the processes causing the observed microstratigraphy in mud-dominant environments.Several prior field observations on continental shelves reveal a variety of seabed states due to wave-current driven sediment transport. The occurrences of these seabed states have several critical implications. For example, the formation of a lutocline indicates trapping of fine sediments near the bed and the resulting large density anomaly may yield significant offshore sediment transport on the shelf through wave-supported gravity flows. When surface waves propagate over a muddy seabed, high wave dissipation rate is often observed during the waning stage of a storm as the fluid mud layer becomes laminarized. A recent microstratigraphy study of mud deposits suggests a three-part sedimentary microfabric that can be associated by processes occur during wave-supported gravity flow events. The main challenges of modeling wave-induced fluid mud transport are the coupling between sediment and turbulence, the transitional nature of turbulent flow, rheology and the polydispersed nature of transport. This research addresses these challenges and the results will be valuable in further interpreting critical processes observed in the mud-dominant coastal environment.The project will improve our understanding of the resuspension and delivery of fine sediment across the continental margin, which is a critical element of the sediment source to sink study. This study will also improve the ability to predict the surface layer properties of the seabed which is critical to underwater exploration and wave prediction. Using wave tanks already available, a hands-on laboratory experiment to visualize the existence of wave boundary layer and the intermittent nature of the mixing process near the bed will be developed by undergraduate students. This newly-designed experiment will be used in Engineering outreach activities taking place annually during the summer session of each institution. In Year 3, this experiment will be added to the curriculum in the undergraduate fluid mechanics laboratory at U. Delaware.

最近的数值研究表明，波浪引起的细颗粒泥沙输移存在四种不同的模式，从良好的混合输运到形成绿跃层，最后在一系列泥沙可利用性和沉降速度范围内完成水流分层。数值模型基于欧拉-欧拉两相公式，简化为细颗粒泥沙(小颗粒响应时间)，同时解决了所有尺度的湍流-泥沙相互作用。该项目将通过数值模拟进一步研究与这些制度有关的四个关键科学问题。首先，通过一系列精心设计的模拟，建立了一个完整的流型图，它是波雷诺数、散体理查森数(泥沙可利用性)和无因次沉降速度的函数。研究结果将突出潮汐边界层和波浪边界层对沉积物响应的主要差异。其次，随着对分层开始的更好的理解，模型将被改进以支持非牛顿流变学，以研究流变应力和湍流调制在决定流型转变和流体动力耗散中的相互作用。第三，将平均电流添加到模拟中。波-流相互作用可能会增加泥层的厚度和运移，最近在新西兰怀亚普河陆架的一项实地研究中观察到这一点。然而，如果水流太强，沉积物可能会被再次夹带，变得很好地混合，从而防止重力流的形成。最后，该模型将扩展到更粗颗粒的运输。本文将首先研究由于波浪雷诺数减小而引起的粘土和粉土的同时输运问题。下一步将使用直接求积矩方法来模拟一个完整的多分散系统。多分散的模拟工作使人们能够深入了解在泥质占优势的环境中导致所观测到的微地层的过程。在大陆架上的几次先前的现场观测揭示了由于波流驱动的沉积物输送而产生的各种海底状态。这些海底状态的出现有几个关键影响。例如，绿跃层的形成表明海床附近的细小沉积物被圈闭，由此产生的大密度异常可能通过波浪支持的重力流在陆架上产生显著的近海沉积物输送。当表面波在泥质海床上传播时，在风暴的减弱阶段，由于漂浮的泥层变得层化，往往会观察到高的波浪消散率。最近一项对泥浆沉积的微地层学研究表明，泥浆沉积微组构由三部分组成，可与波浪支持的重力流事件期间发生的过程联系在一起。模拟波浪引起的泥浆输运的主要挑战是泥沙和湍流之间的耦合、湍流的过渡性、流变学和输运的多分散性。这项研究解决了这些挑战，其结果将对进一步解释在泥质占优势的沿海环境中观察到的关键过程有价值。该项目将提高我们对大陆边缘细颗粒沉积物再悬浮和输送的理解，这是沉积物来源到下沉研究的关键要素。这项研究还将提高预测海底表层性质的能力，这对水下勘探和波浪预报至关重要。使用已有的波浪箱，本科生将开发一项动手实验室实验，以直观地显示波边界层的存在和床层附近混合过程的间歇性。这项新设计的实验将用于每年各机构夏季会议期间举行的工程学外展活动。在第三年，这个实验将被添加到特拉华大学本科生流体力学实验室的课程中。