Collaborative Research: LES and RANS simulations of estuarine flows: Understanding and parameterizing the role of Langmuir turbulence

朗缪尔环流被认为是成对的平行反向旋转的涡（或单元），大致沿风向定向，表征了上层海洋、湖泊和河口内的波浪和风驱动的湍流（即朗缪尔湍流）。它在湖泊和河口的作用缺乏了解。该项目的总体目标是提供一个精细尺度的数值研究朗缪尔环流，其与其他相干流结构的相互作用，以及由此产生的影响河口内的垂直混合和横向扩散。河口被简单地定义为淡水和盐水混合的沿海地区。河口生态系统是世界上最具生产力的生态系统之一，由无数的栖息地组成，包括牡蛎礁、珊瑚礁、水下水生植被、沼泽和红树林。建议的数值模拟将提高对河口生态系统有直接影响的流动动力学的理解。这些动态支配着水成分的空间分布，如溶解有机物、浮游植物、悬浮沉积物和影响河口生态系统健康的溢出污染物。 拟议的研究包括大涡模拟（LES）的亚中尺度相干流结构，如前和涡流和较小尺度的风和波驱动的朗缪尔环流在理想化的河口设置之间的相互作用。大涡模拟将被用来研究理想化的潮汐入侵锋进入河口和理想化的河流羽流传播通过河口和排放到沿海海洋。LES将允许调查（a）河口和沿海海洋之间的交流，通过潮汐入侵前和河流羽流和（B）朗缪尔环流及其相互作用的作用引起的湍流混合的作用与涡流和前确定整个河口的横向和垂直混合。LES将允许改进的湍流闭合的发展，能够占垂直混合的朗缪尔湍流制度。这些封闭模型将用于理想化流动的雷诺平均纳维尔-斯托克斯（RANS）模拟，并将这些结果与LES进行比较。这将允许在存在朗缪尔环流的情况下评估RANS方程的当前湍流闭合。(3)更新湍流闭合，以考虑RANS模拟中的朗缪尔湍流。到目前为止，在粗尺度河口流模拟中，三维RANS方程还没有实现朗缪尔湍流闭合。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Langmuir circulation is recognized as pairs of parallel counter-rotating vortices (or cells) oriented approximately in the direction of the wind, characterizing the wave- and wind-driven turbulence (i.e. the Langmuir turbulence) within the upper ocean, lakes and estuaries. Its role in lakes and estuaries lacks understanding. The overarching goal of this project is to provide a fine-scale numerical study of Langmuir circulation, its interaction with other coherent flow structures and the resulting influence on vertical mixing and lateral dispersion within estuaries. Estuaries are briefly defined as coastal areas where freshwater and saltwater mix. Estuarine ecosystems are one of the most productive in the world made up of a myriad of habitats including oyster reefs, coral reefs, submerged aquatic vegetation, marshes and mangroves. The proposed numerical simulations will enhance understanding of flow dynamics that have direct impact on estuarine ecosystems. These dynamics govern the spatial distribution of water constituents such as dissolved organic matter, phytoplankton, suspended sediments and spilled contaminants that influence the health of estuarine ecosystems. The proposed studies consist of large-eddy simulations (LES) of the interaction between submesoscale coherent flow structures such as fronts and eddies and the smaller scale wind and wave-driven Langmuir circulation in idealized estuarine settings. LES will be used to investigate the idealized tidal intrusion front entering an estuary and an idealized river plume propagating through an estuary and discharging to a coastal ocean. The LES will allow investigations of (a) the role of turbulent mixing induced by Langmuir circulation in exchanges between the estuary and the coastal ocean via tidal intrusion fronts and river plumes and (b) the role of Langmuir circulation and its interaction with eddies and fronts determining the lateral and vertical mixing throughout the estuary. LES will allow for the development of improved turbulence closures able to account for the vertical mixing of the Langmuir turbulence regime. These closure models will then be used in Reynolds-averaged Navier-Stokes (RANS) simulations of the idealized flows and these results will be compared with the LES. This will allow for assessment of current turbulence closures for the RANS equations in the presence of Langmuir circulation. (3) Turbulence closures will be updated to account for Langmuir turbulence in RANS simulations. To date Langmuir turbulence closures have not been implemented for the three-dimensional RANS equations in coarse-scale estuarine flow simulations.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.