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Route to turbulence in Strongly Stratified Slope Flows

强层化斜坡流中的湍流路径

基本信息

批准号：
1936445
负责人：
Inanc Senocak
金额：
$ 36.28万
依托单位：
University of Pittsburgh
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-09-01 至 2023-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1936445&HistoricalAwards=false
关键词：
Route turbulence Strongly Stratified Slope

项目摘要

Turbulence, or high-speed chaotic fluid motion, is the norm rather than the exception in nature. Describing and predicting fluid turbulence is complex and requires computer simulations. Many advances have been achieved in computer modeling of turbulence under well-mixed atmospheric flow conditions. However, a serious concern in weather forecasting has been inadequate modeling of turbulence within a stratified atmosphere and in regions of complex terrain. In a stratified atmosphere, buoyancy force (due to density variations) acts in the same direction as gravity, hindering the formation of well-mixed flow conditions. Stratified conditions are commonly observed during nighttime in mountainous terrain and over large ice sheets and glaciers. Accurate prediction of winds (air flow) over Antarctica and Greenland is an important aspect of understanding the impact of climate change, because the strength and structure of winds are directly connected to the ablation of ice sheet and the associated sea level rise. Moreover, prediction of nocturnal winds in mountainous terrain has important implications for air quality, agriculture, and defense operations. This project is expected to lead to improved prediction of winds under stratified conditions in computer models of weather. Outreach activities are planned for existing precollege preparatory programs. The project will result in open-source educational materials related to stratified fluid turbulence.The chief technical objective is to investigate newly discovered fluid instabilities over sloping terrain and unravel their role in progression toward an intermittent and patchy turbulent state. Inclination of the surface alters the turbulence dynamics due to obliqueness of stratification relative to flow shear, leading to further departure from a classical boundary layer profile. The project will adopt contemporary techniques from hydrodynamic stability theory and direct numerical simulations to arrive at an atlas of fluid instabilities as a function of the surface inclination and the newly introduced dimensionless stratification perturbation parameter. The investigation is expected to reveal new flow features emerging at sufficiently high stratification perturbation numbers and improve the comprehension of flow intermittency in the form of bursting phenomena and patchy turbulence. The project will culminate with a quantitative criterion to characterize intermediate flow regimes that range from laminar to fully turbulent conditions, thus filling the current knowledge gap pertinent to partially turbulent stratified slope flows. The outcomes of this project are expected to lead to future improvements of subgrid-scale parameterizations of stably stratified conditions in numerical weather prediction models.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.

湍流，或高速混沌流体运动，是自然界的常态，而不是例外。描述和预测流体湍流是复杂的，需要计算机模拟。在充分混合的大气流动条件下紊流的计算机模拟方面取得了许多进展。然而，天气预报中的一个严重问题是对分层大气和复杂地形地区湍流的模拟不足。在分层大气中，浮力（由于密度变化）与重力方向相同，阻碍了混合良好的流动条件的形成。夜间在山区、大冰原和冰川上通常观察到分层现象。准确预测南极洲和格陵兰岛上空的风（气流）是了解气候变化影响的一个重要方面，因为风的强度和结构与冰盖的消融和相关的海平面上升直接相关。此外，山区夜间风的预测对空气质量、农业和国防行动具有重要意义。这一项目有望提高计算机天气模型在分层条件下对风的预测。计划为现有的大学预科课程开展外展活动。该项目将产生与分层流体湍流相关的开源教育材料。主要的技术目标是研究倾斜地形上新发现的流体不稳定性，并揭示它们在向间歇性和斑块状湍流状态发展过程中的作用。由于相对于流动切变的分层倾斜，表面的倾斜改变了湍流动力学，导致进一步偏离经典边界层剖面。该项目将采用流体动力稳定性理论和直接数值模拟的当代技术，以获得作为表面倾角和新引入的无量纲分层摄动参数函数的流体不稳定性图谱。该研究有望揭示在足够高的分层扰动数下出现的新流动特征，并提高对破裂现象和斑块湍流形式的流动间歇性的理解。该项目最终将获得一个定量标准，以表征从层流到完全湍流的中间流动状态，从而填补目前与部分湍流分层斜坡流动相关的知识空白。该项目的结果有望导致数值天气预报模式中稳定分层条件的亚网格尺度参数化的未来改进。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。