The Role of Inlet Perturbations on Superstructures of Turbulent Boundary Layers- Toward Global Flow Control

这个提议是关于紊流中一个非常基本的问题的研究，即固体壁面附近的小流量变化对下游非常长的涡流发展的影响。这种理解的实际结果将是有可能通过对上游流动的微小修改来控制下游的湍流，从而导致工业应用的改进，例如膜冷却技术，商业和军事飞行，风能涡轮叶片的设计以及在固体表面上泵送的流体湍流的情况下节省能源。虽然紊流边界层的研究已经有50多年的历史，但对它的理解仍然是紊流学界争论的原因。然而，如果我们要开发实用的控制方案来帮助减轻湍流边界层的能量损失，这种理解是至关重要的。近年来的研究表明，存在着大尺度运动（Large Scale movements, lsm）和甚大尺度运动（Very Large Scale movements, vlsm），它们承载着超过50%的雷诺应力和动能。这些运动中最大的运动有0 (1δ) &#8804；L, # 8804;O(10δ)，通常也被称为上层建筑。本研究的假设是证明通过操纵入口条件来控制“上层建筑”来实现下游流动的全局流动控制的可能性。我们来自美国和澳大利亚的团队试图解释这种复杂相互作用的机制，并探索这些上层建筑如何调节内部区域，反之亦然。本研究由高雷诺数风洞实验和高保真直接数值模拟（DNS）组成，研究不同进口扰动（如定常和非定常）影响下空间发展的湍流边界层。低雷诺数模拟将揭示入口扰动对上层结构的影响，并将为中等和高雷诺数研究提供最佳配置。通过与PI于2013年建立的正在进行的暑期研究所的协同作用，将促进学生的招募和推广。此外，还将与波多黎各的院校建立联系，在那里，联合私立学校在招生方面有着良好的记录。PIs还计划在资助期间每年夏天让K-12教师参加风能湍流研讨会。

This proposal is about the investigation of a very fundamental issue in turbulent flows, the issue of the effects of small flow changes close to a solid wall on the development of very long eddies farther downstream. The practical outcome of such understanding would be the possibility to control turbulence downstream by small modifications of the flow upstream, leading to improvements in industrial applications, such as film cooling technology, commercial and military flight, design of wind energy turbine blades and saving energy in cases where fluid pumped over a solid surface is turbulent. Although turbulent boundary layers have been studied for over 50 years, the understanding of them remains the cause of ontroversy in the turbulence community. Such understanding is critical, however, if we are to develop practical control schemes that can help mitigate the energy penalty of turbulent boundary layers. Recent studies have shown that there are Large Scale Motions (LSMs) and Very Large Scale Motions (VLSMs) that carry more than 50% of the Reynolds stresses and kinetic energy. The largest of these motions have scales of the order of O(1δ) ≤ L ≤ O(10δ) and are often also referred to as superstructures. The hypothesis in the proposed study is to demonstrate the possibility to achieve Global Flow Control of the downstream flow by manipulating the inlet conditions in such a way to control the "superstructures". Our team from the USA and Australia seeks to explain the mechanisms by which such complex interactions are possible, and also to explore how these superstructures can modulate the inner region and vice versa. The proposed research consists of high Reynolds number wind tunnel experiments and high fidelity Direct Numerical Simulations (DNS) to study spatially-developing turbulent boundary layers under the influence of different inlet perturbations (e.g., including steady and unsteady). The low Reynolds number simulations will uncover the impact of inlet perturbations on superstructures and will provide optimum configurations to consider in the moderate and high Reynolds number studies. Recruitment of students and outreach will be facilitated by synergies with the ongoing Summer Research Institute established by the PI in 2013. In addition, there will be links to Puerto Rico institutions, where the co-PIs have a strong track record of student recruitment. The PIs also have a plan bringing K-12 teachers to Workshop on Wind Energy Turbulence each summer for the duration of the grant.