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

Langmuir环流被认为是一对平行的反旋转涡旋（或单体），其方向大致与风向一致，表征了上层海洋、湖泊和河口内由波浪和风驱动的湍流（即Langmuir湍流）。它在湖泊和河口的作用尚不清楚。该项目的总体目标是提供朗缪尔环流的精细尺度数值研究，它与其他相干流结构的相互作用以及由此产生的对河口内垂直混合和横向分散的影响。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。提出的数值模拟将加强对对河口生态系统有直接影响的流动动力学的认识。这些动态控制着影响河口生态系统健康的溶解有机物、浮游植物、悬浮沉积物和溢出污染物等水成分的空间分布。在理想的河口环境下，采用大涡模拟的方法研究了锋面、涡流等亚中尺度相干流结构与较小尺度风浪驱动的Langmuir环流之间的相互作用。LES将用于研究进入河口的理想潮汐入侵锋和通过河口传播并排放到沿海海洋的理想河羽。LES将允许调查(a)由朗缪尔环流引起的湍流混合在河口和沿海海洋通过潮汐入侵锋和河流羽流交换中的作用；(b)朗缪尔环流的作用及其与漩涡和锋的相互作用决定了整个河口的横向和垂直混合。LES将允许开发改进的湍流闭包，能够解释Langmuir湍流状态的垂直混合。这些闭合模型随后将用于理想化流动的reynolds -average Navier-Stokes （RANS）模拟，并将这些结果与LES进行比较。这将允许在Langmuir环流存在的情况下评估RANS方程的当前湍流闭包。(3)湍流闭包将更新，以考虑RANS模拟中的Langmuir湍流。迄今为止，在粗尺度河口流动模拟中尚未对三维RANS方程实现Langmuir湍流闭包。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。

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.