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

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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.