CAREER: High fidelity numerical simulations of turbulent flow separation at high Reynolds numbers with passive scalar transport.

拟议的研究将提供关于流体动力学问题的基础知识，该问题尚未得到很好的理解：流动分离及其与热量和污染物传输的关联。 当流体流过物体（例如，飞机机翼）突然从表面“脱离”。 然后，在分离区域中形成称为尾流或涡流的旋流运动，这导致物体上的流体阻力增加。流动分离是不希望的，并且会严重降低诸如飞机和涡轮机的工程设备的性能。高分辨率数值模拟的使用将允许更有效的湍流模型的进步。这些模型将促进流动、热量和污染物输运控制工具的发展，以减轻不必要的流动分离效应。拟议的研究和教育目标将在位于波多黎各联邦的西班牙裔服务机构进行。该项目的教育部分促进了高性能计算，计算思维和建模的使用。这些概念将被引入到本科和研究生课程使用翻转课堂的概念。处理后的数据和产生的代码将向公众开放，供分析和验证。此外，一个计算和可视化设施将被开发为研究，学习和推广部门夏令营的K-12学生和教师的工具。 本研究的主要目的是数值阐明被动标量现象背后的细节在边界层分离过程中，从两个最常见的原因造成的流动分离：流向和壁曲率驱动的压力梯度，在组合和孤立的形式。这项研究将涵盖几乎整个频谱，特别是在近壁区，实验技术和湍流模型表现出严重的局限性。通过识别和跟踪拉格朗日相干结构（LCS），探索LCS运动学和被动标量场之间的关系，它可能会准确地解释分离过程。这些研究工作将使用巨大的计算资源，需要最先进的千万亿次，并行和图形处理单元（GPU）编程。具体目标包括：i）在实验雷诺数下，对强减速条件下的空间发展湍流边界层进行直接数值模拟（DNS），ii）通过低阶/高阶统计分析了解分离过程中的传输现象，并使用iOS/Android应用程序沿着创建LCS数据库，用于增强/虚拟现实，iii）在大涡模拟（LES）中开发一种独特的数据驱动的亚网格尺度（SGS）建模，重点关注被动标量的未知领域。该项目由流体动力学计划和激励竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了NSF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。

The proposed research will provide foundational knowledge on an issue in fluid dynamics that is not well understood: flow separation and its association with heat and contaminant transport. Flow separation occurs when fluid flow past an object (e.g., wing of an aircraft) abruptly "detaches" from the surface. A swirling motion, called wakes or vortices, is then formed in the separated region which result in increasing the fluid drag force on the object. Flow separation is unwanted and can seriously reduce performance of engineered devices such as aircraft and turbines. The use of high-resolution numerical simulations will permit the advancement of more efficient turbulence models. Such models will facilitate the development of flow, heat, and contaminant transport control tools to mitigate unwanted flow separation effects. The proposed research and educational objectives will be carried out at a Hispanic Serving Institution, located in the Commonwealth of Puerto Rico. The educational component of this project promotes the use of high-performance computing, computational thinking, and modeling. Such concepts will be introduced to undergraduate and graduate courses using flipped classroom concept. The post-processed data and resulting codes will be made accessible to the public for analysis and validation. Additionally, a computing and visualization facility will be developed as a tool for research, learning, and outreach in departmental Summer Camps for K-12 students and teachers. The principal aim of this study is to numerically elucidate the details behind passive scalar phenomena during boundary layer separation, resulting from the two most frequent causes of flow detachment: streamwise and wall-curvature driven pressure gradient, in combination and isolated forms. The study will cover nearly the entire spectrum, particularly in the near wall region, where experimental techniques and turbulence models exhibit severe limitations. By identifying and tracking Lagrangian Coherent Structures (LCS) and exploring the relationship between LCS kinematics and passive scalar fields, it may be possible to accurately explain the separation process. These research efforts will apply the use of tremendous computational resources, requiring state-of-the-art petascale, parallel and Graphics Processing Unit (GPU) programming. Specific objectives include i) perform Direct Numerical Simulation (DNS) of spatially-developing turbulent boundary layers under strong deceleration at experimental Reynolds numbers, ii) understand the transport phenomena in the separation process by means of low/high order statistics analysis and create an LCS data bank along with iOS/Android apps for augmented/virtual reality, iii) develop a unique data-driven modeling of sub-grid scale (SGS) in Large Eddy Simulation (LES), focusing on the uncharted area of passive scalar. This project is jointly funded by the Fluid Dynamics Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.