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.

最近的数值研究揭示了波浪诱导的细沉积物运输的四个不同的机制，从混合良好的运输，到lutocline的形成，以及最终在一系列沉积物的可用性和沉降速度上完全流动层流化。数值模型基于简化用于细胞沉积物（小粒子响应时间）的Eulerian-Eulerian两相配方，同时解决了所有湍流 - 补充相互作用的尺度。该项目将通过数值模拟进一步调查与这些制度有关的四个关键科学问题。首先，将通过流程度来构建完整的相位图，这是Wave Reynolds编号，批量Richardson编号（储藏式可用性）和一系列经过精心设计的模拟的函数的函数。结果将突出响应沉积物响应潮汐和波边界层之间的主要差异。其次，有了更好地了解层流化的发作，该模型将得到增强以支持非牛顿流变学，以研究流变应力和湍流调节之间的相互作用，以确定流动状态和流体动力耗散的过渡。第三，平均电流将添加到模拟中。如最近在怀亚浦河（新西兰）的架子上观察到的，波动 - 电流相互作用可能会增强泥土层的厚度和运输。但是，如果电流太强，则可以重新排入沉积物并变好，因此可以防止重力流的形成。最后，该模型将扩展以进行更粗的谷物运输。首先研究由于波浪雷诺数减少而导致的粘土和淤泥的同时运输。下一步将是使用矩方法的直接正交方法模拟完整的多分散系统。多分散的模拟工作可以深入了解导致泥浆式环境中观察到的微地层学的过程。大陆架子上的几个先前的现场观察结果揭示了由于波流驱动的沉积物传输而引起的各种海底状态。这些海床状态的发生有几个关键含义。例如，lutocline的形成表明在床附近捕获细小的沉积物，所得的大密度异常可能会通过波浪支持的重力流在架子上产生明显的近海沉积物传输。当表面波在泥泞的海床上传播时，随着流体泥土层变得层流，通常在暴风雨的衰弱阶段观察到高波浪耗散率。泥土沉积物的最新一项微地层研究表明，在波浪支持的重力流动事件期间，可以通过过程与过程相关的三部分的沉积微结构。建模波诱导的流体泥浆传输的主要挑战是沉积物与湍流之间的耦合，湍流的过渡性质，流变学和运输的多分散性质。这项研究解决了这些挑战，结果对于进一步解释在泥泞的沿海环境中观察到的关键过程将是有价值的。该项目将提高我们对在大陆边缘的重悬于和交付精美沉积物的理解，这是这是这是关键因素，这是沉积物的沉积物来源。这项研究还将提高预测海底表面层特性的能力，这对于水下勘探和波浪预测至关重要。使用已经可用的波罐，一个动手实验室实验可视化波浪边界层的存在，并且床附近的混合过程的间歇性质将由本科生开发。这个新设计的实验将用于每家机构的夏季课程每年进行的工程外展活动。在第3年，该实验将添加到美国特拉华州大学的本科流体力学实验室的课程中。