CAREER: High-Speed Boundary Layer Transition on Realistic Non-Smooth Surfaces

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。对于高效高速车辆的设计，准确预测流场及其与固体表面的相互作用是至关重要的。在湍流（非有序运动）流动中，表面摩擦和传热明显高于层流（有序运动）流动，导致性能损失和潜在的临界失效。准确的层流到湍流过渡预测是流体动力学研究中的一个关键挑战，因为它取决于与几何形状、流动条件、外部干扰环境和表面光滑度相关的许多参数。在高速下，暴露在热的、快速移动的流体中会导致烧蚀过程中严重的表面退化。因此，彻底了解这些现实的非光滑表面如何影响过渡对于准确的流动预测至关重要。该项目通过研究时间演变（烧蚀）粗糙表面与高速过渡流的相互作用，解决了基础研究知识的明确空白。这项研究可以产生更广泛的积极影响，例如，它可以实现涉及流体流动的更节能的工程系统，允许更有效的空间探索，有朝一日可以实现商业高超音速飞行和其他形式的高速运输，以及提供对国家安全至关重要的快速响应能力。该项目还将包括重要的教育活动，鼓励学生从事STEM学科的职业，包括在几项外展工作中使用的基于计算机的学习经验，重点是教授计算技能。科学研究的目的是获得对实际非光滑表面如何影响层流到湍流过渡过程的所有阶段的基本理解。该项目通过将过渡流与现实时间演变（烧蚀）表面的相互作用纳入其中，远远超出了当前的最先进技术。本文将进行首次考虑高超声速边界层转捩的耦合流-烧蚀相互作用模拟。这些模拟将提供深入了解所涉及的复杂物理现象的复杂性。这些模拟将采用一种独特的数值方法，捕捉广泛的时间和空间尺度，并使用先进的分析工具，如模态和双正交分解，来剖析复杂的物理现象，并培养对涉及广泛参数空间的不同效应的理解。这项研究将产生前所未有的理解，对于提高过渡预测能力和提供对现实高速流动环境的过渡过程进行批判性评估的能力至关重要。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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). For the design of efficient high-speed vehicles, it is essential to accurately predict the flow field and its interaction with solid surfaces. In the presence of turbulent (non-orderly moving) flow, surface friction and heat transfer are significantly higher than for laminar (orderly moving) flow, leading to performance losses and potentially critical failure. Accurate laminar-to-turbulent transition prediction is a key challenge in fluid dynamics research as it depends on many parameters associated with the geometry, flow conditions, external disturbance environment and smoothness of the surface. At high speeds, exposure to hot, fast-moving flow can lead to severe surface degradation through ablation processes. Therefore, a thorough understanding of how these realistic non-smooth surfaces affect transition is essential for accurate flow predictions. This project addresses a definite gap in fundamental research knowledge by investigating the interaction of time-evolving (ablative) rough surfaces with high-speed transitional flows. This research can have a significant broader positive impact as it can, for example, enable more energy efficient engineering systems involving fluid flows, allow for more efficient space exploration, one day enable commercial hypersonic flight and other forms of high-speed transportation as well as provide rapid response capabilities essential for national security. The project will also encompass significant educational activities encouraging students to pursue careers in STEM disciplines, including computer-based learning experiences used in several outreach efforts with a focus on teaching computational skills.The scientific research objective is to obtain a fundamental understanding of how realistic non-smooth surfaces affect all stages of the laminar-to-turbulent transition process. This project goes well beyond the current state-of-the-art by including the interaction of transitional flows with realistic time evolving (ablative) surfaces. The first ever coupled fluid-ablation interaction simulations considering hypersonic boundary layer transition will be performed. These simulations will provide insight into the intricacies of the complex physical phenomena involved. A unique numerical approach capturing the wide range of temporal and spatial scales will be employed for these simulations and advanced analysis tools, such as modal and bi-orthogonal decomposition, will be used to dissect the complex physics and cultivate understanding of the different effects involving a wide parameter space. This research will yield unprecedented understanding essential for improving transition prediction capabilities and for providing the ability to critically assess the transition process for realistic high-speed flow environments.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.