Turbulence Closure for Energetic, low-Ri Stratified Shear Flows

在科学和实际应用中至关重要的分层低理查森数剪切流对湍流闭合提出了很高的要求。将采用现有的封堵器，并在必要时对其进行修改，对现有封堵器进行三步筛选，从而开发出一种能够真实模拟这种流动的紊流封堵器模型。第0步要求封闭件对于均匀分层剪切流具有实际的稳定状态，例如在货车Atta小组的实验室实验中。在第1步中，封闭件在模拟和观察到的湍流耗散率和长度尺度的严格定量比较中进行隔离测试。第1步的观测基础是潮汐驱动的哈德逊河口的大量微观结构测量。在步骤1中对封闭物的要求是，给定观测到的剪切和浮力频率，封闭物产生与观测到的湍流混合的水平和潮汐深度-时间结构的紧密匹配。在第2步中，将封闭物嵌入红海盐水流出的2D和3D数值模型中。这里的封闭的要求是，它允许的数值模型，以重现流出的特殊结构相结合的核心层在底部，经历了小夹带和稀释超过100公里的距离，而厚剪切区以上的核心层经历高能湍流混合。将探讨在非流体静力学2D模型和较粗分辨率的流体静力学3D模型中封闭件性能的差异。3D模型允许调查旋转和流出通道地形的可能影响。将考虑的闭合方案包括Baumert和Peters的新闭合，Canuto等人的闭合，其在修改后通过步骤0，Peters等人和梅洛尔以前使用的另一种封闭物，拟议研究的更广泛影响将通过改善沿海和河口沃茨的管理以及对气候和气候变化的研究来实现，最广泛使用的模型中嵌入的湍流封闭改进的结果。教育部分是通过一名研究生的拟议参与提供的。

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.