Turbulence Closure for Energetic, low-Ri Stratified Shear Flows

分层、低理查德森数剪切流在科学和实践中具有重要意义，对湍流闭流提出了很高的要求。一个能够真实地模拟这种流动的湍流闭合模型将会被开发出来，如果必要的话，修改现有的闭合，并将它们置于三步筛选过程中。第0步是要求闭包对于均匀、分层的剪切流具有现实的稳定状态，如Van Atta小组的实验室实验。在步骤1中，封闭测试在模拟和观测湍流耗散率和长度尺度的严格定量比较隔离。第1步的观测基础是来自潮汐驱动的哈德逊河河口的大量微观结构测量。步骤1中对闭包的要求是，给定观测到的剪切和浮力频率，闭包与观测到的湍流混合的水平和潮汐深度-时间结构密切匹配。在第二步中，封闭体被嵌入到红海盐水流出的二维和三维数值模型中。这里对闭合的要求是，它允许数值模型重现流出的特殊结构，该结构结合了底部的核心层，在超过100公里的距离上经历了很少的夹带和稀释，而核心层上方的厚剪切带经历了高能湍流混合。在非流体静力2D模型和较粗分辨率的流体静力3D模型中，将探讨闭包性能的差异。3D模型允许研究旋转和流出通道地形的可能影响。将考虑的闭包方案包括Baumert和Peters的新闭包，Canuto等人在修改后通过第0步的闭包，Peters等人和Mellor/Yamada之前使用的另一种闭包，这种闭包正在普遍使用。拟议研究的更广泛影响将是通过改善沿海和河口水域的管理，以及对气候和气候变化的研究，这是由于大多数广泛使用的模型中嵌入的湍流封闭的改进。一个教育的组成部分是通过一个研究生的建议参与。

ABSTRACTOCE-0352047Stratified, low-Richardson number shear flows, which are of crucial importance in scientific and practical contexts, place high demands on turbulence closures. A turbulence closure model that can realistically simulate such flows will be developed by taking, and if necessary modifying, existing closures and to subjecting them to a three-step screening process. Step 0 is a demand that the closures have a realistic steady state for homogeneous, stratified shear flows such as in the laboratory experiments of Van Atta's group. In Step 1 the closures are tested in isolation in a strict quantitative comparison of simulated and observed turbulent dissipation rates and length scales. The observational basis of Step 1 are extensive microstructure measurements from the tidally driven Hudson River estuary. The demand on the closures in Step 1 is that, given the observed shear and buoyancy frequency, the closures produce a close match of the levels and tidal depth-time structure of the observed turbulent mixing. In Step 2 the closures are embedded in 2D and 3D numerical models of the outflow of saline water from the Red Sea. The demand on the closure here is that it allow the numerical models to reproduce the peculiar structure of the outflow which combines a core layer at the bottom that undergoes little entrainment and dilution over a distance of over 100 km while a thick shear zone above the core layer undergoes highly energetic turbulent mixing. The difference in performance of the closures in a non-hydrostatic 2D model and a coarser-resolution, hydrostatic 3D model will be explored. The 3D model allows investigating possible effects of rotation and of the outflow channel topography. The closure schemes which will be considered include the new closure by Baumert and Peters, the Canuto et al. closure which passes Step 0 after modification, another closure previously employed by Peters et al. and Mellor/Yamada which is being used ubiquitously.The broader impacts of the proposed research will be through improved management of coastal and estuarine waters as well as research into climate and climate change as a result of improvement of turbulence closures embedded in most widely used models. An educational component is given through the proposed participation of a graduate student.