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

这个建议是关于湍流中一个非常基本的问题的研究，即靠近固体壁的小流量变化对下游很长涡流发展的影响。这种理解的实际结果将是通过对上游流动的微小修改来控制下游湍流的可能性，从而导致工业应用中的改进，例如薄膜冷却技术、商业和军事飞行、风能涡轮机叶片的设计以及在固体表面上泵送的流体是湍流的情况下的节能。虽然湍流边界层的研究已经有50多年的历史，但对它们的理解仍然是湍流界争议的原因。然而，如果我们要发展实际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。最近的研究表明，有大尺度运动（LSMs）和超大尺度运动（VLSMs），携带超过50%的雷诺应力和动能。这些运动中最大的运动具有O（1 #948;）#8804; L #8804; O（10 #948;）量级的尺度，并且通常也被称为超结构。在拟议的研究中的假设是证明的可能性，以实现整体流量控制的下游流量，通过操纵入口条件，以这种方式来控制“上层建筑”。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可能机制，并探索这些超级结构如何调节内部区域，反之亦然。拟议的研究包括高雷诺数风洞实验和高保真直接数值模拟（DNS），以研究不同入口扰动（例如，包括稳定的和不稳定的）。低雷诺数模拟将揭示入口扰动对上部结构的影响，并将提供在中等和高雷诺数研究中考虑的最佳配置。将通过与PI于2013年建立的正在进行的暑期研究所的协同作用促进学生的招募和外联。此外，将有链接到波多黎各机构，在那里的共同PI有一个强大的学生招聘记录。PI还计划在赠款期间每年夏天将K-12教师带到风能湍流研讨会。

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.