CAREER: Turbulence in a rapidly changing world

靠近车辆表面的空气或水的流动是复杂的，对车辆的性能至关重要。这些“边界层”流动是阻力的主要来源，特别是在机动过程中，控制着流动路径与车辆几何形状的密切程度，这可以极大地改变车辆所承受的力。前人对恒风条件下大型车辆的边界层流动和非定常机动时小型车辆的边界层流动进行了大量的研究，但对非定常条件下大型车辆的边界层流动研究甚少。为了在大风或波浪条件下设计和安全操纵大型车辆，需要更多的基本知识来了解它们的边界层如何对加速和减速做出反应。该项目创造了新的实验能力，并利用这些能力来研究边界层的加速和减速，从而从根本上了解由于不稳定而导致的行为变化。这项工作将把研究结果整合到伊利诺伊大学厄巴纳-香槟分校的课程中，并将通过教育正义项目的数学辅导项目使丹维尔惩教中心的在押学生受益。该项目将推进加速边界层的知识和实验能力。流动加速度有一个阈值，低于这个阈值可以不考虑加速度而预测流量，超过这个阈值，加速度就会定性地改变物理行为。该项目将量化三种配置的阈值及其对流量参数的依赖。流动对加速和减速的反应不同，项目将量化和理解这些对边界层的不同影响。最后，经过一次加速后，水流恢复到稳态；该项目将量化这一复苏的性质。对阈值、迟滞和恢复的理解和观察将成为科学理解和预测加速湍流边界层的基础。该项目还将推进最先进的实验能力，以研究时间加速边界层。利用新颖的、快速可重构的几何结构，该项目将产生高雷诺数、非定常流场条件。科学发现将作为北约先进车辆技术工作组的一部分进行共享。该项目还支持在丹维尔惩教中心为在押学生建立分层数学教学项目。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。

The flow of air or water very near the surface of vehicles is complex and is crucial to the performance of a vehicle. These "boundary layer" flows are a major source of drag and, especially during maneuvers, control how closely the flow’s path follows the geometry of the vehicle, which can dramatically change the forces that the vehicle experiences. While significant prior work has been done on boundary layer flows for large vehicles under constant wind conditions, and on boundary layer flows for very small vehicles during unsteady maneuvers, little work has been done on boundary layer flows for large vehicles under unsteady conditions. To design and safely maneuver large vehicles in gusty or wavy conditions, more fundamental knowledge is needed about how their boundary layers respond to accelerations and decelerations. This project creates new experimental capabilities and uses those capabilities to study boundary layers accelerating and decelerating to fundamentally understand changes in behavior due to unsteadiness. The work will integrate the findings into courses at the University of Illinois Urbana-Champaign and will benefit incarcerated students at the Danville Correctional Center through a math tutoring program with the Education Justice Project.The project will advance knowledge and experimental capabilities for accelerating boundary layers. There is a threshold on the rate of flow acceleration, below which the flow can be predicted without accounting for the acceleration, and above which the acceleration qualitatively changes the physical behavior. The project will quantify that threshold and its dependence on flow parameters for three configurations. The flow responds differently to accelerations and decelerations and the project will quantify and understand these different effects on the boundary layer. Finally, after an acceleration the flow recovers to a steady state; the project will quantify the nature of that recovery. Together, the understanding and observation of thresholds, hysteresis, and recovery will form a basis for scientific understanding and prediction of accelerating turbulent boundary layers. The project will also advance the state-of-the-art in experimental capabilities for studying temporally accelerating boundary layers. Using novel, rapidly reconfigurable geometries the project will generate high-Reynolds number, unsteady flow conditions. Scientific findings will be shared as part of a NATO advanced vehicle technologies working group. The program also supports the formation of a tiered math teaching program at Danville Correctional Center for incarcerated students.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.