Collaborative Research: Reaping the Whirlwind: Re-energizing Boundary Layers by Targeted Manipulation of Coherent Structures

在湍流中，例如在飞机机翼表面附近或在大气中，当它流经地球表面时，会有一系列不同大小的涡流。其中最大的相干涡旋，称为大尺度运动(LSM)，携带了湍流动能的很大一部分，并在很大程度上负责混合远离地面的高速流动和靠近地面的低速流动。这种混合可以通过选择性地向表面移位LSM来增强，这在某些应用中是非常理想的。例如，将高速气流带到表面可以防止机翼失速和失去升力。该项目的目标是通过模拟和匹配实验证明一种探测和操纵LSM以重新激发近地表流动的方法。本方法的成功还有望推动出现控制水下、地面飞行器或飞行器的声学噪声或热传递或涡轮机械燃烧等技术。因此，该项目有可能开创湍流控制的新方向。这项研究的目的是开发一个经过实验验证的系统，用于主动探测和操纵湍流边界层再激励的LSM。对LSM的基本理解的进步、执行器的创新和先进的控制理论使这一目标得以实现。迈向这一目标的第一步是通过在协调良好的边界层实验和直接数值模拟(DNS)中操纵受控的、特征良好的、合成生成的结构来演示为边界层提供能量。初步试验成功地演示了采用两种不同控制方法的控制射流驱动的最优化，使原型LSM偏向表面。初步工作已经创造了一种基于合成喷气的合适的执行器，并在实验室中进行了演示。在这个为期3年的合作项目中提出的具体任务是：(1)开发和实施控制算法，以在匹配实验和域名系统中选择性地移动合成生成的LSM，(2)量化通过移动不同类型的LSM实现的再能量，以指导目标优先顺序，以及(3)测试和优化湍流边界层的再能量，着眼于分离控制和风力发电应用。该项目的成果将通过在线平台和加强课堂活动向公众公布。该项目还将帮助从代表性不足的群体中招收研究生和几个本科生研究项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In a turbulent flow, for example near the surface of an airplane wing or in the atmosphere as it flows over the Earth’s surface, there is a range of eddies of different sizes. The largest of these coherent eddies, called Large Scale Motions (LSMs), carry a significant portion of the turbulent kinetic energy and are largely responsible for mixing high-speed flow far away from the surface with the low-speed flow right near the surface. This mixing may be enhanced by selectively displacing the LSMs toward the surface, and this is very desirable in some applications. For example, bringing high-speed flow to the surface can keep a wing from stalling and losing its lift. The goal of this project is to prove via simulations and in matched experiments an approach to detect and manipulate LSMs to re-energize the near-surface flow. The success of the present approach is also expected to motivate the emergence of technologies such as controlling acoustic noise or heat transfer for underwater, ground-vehicles, or air-vehicles or combustion in turbomachinery. This project thus has the potential of initiating a new direction in turbulent flow control. The goal of this research is to develop an experimentally-validated system for active detection and manipulation of LSMs for turbulent boundary layer re-energization. Advances in the fundamental understanding of LSMs, actuator innovations, and advanced control theory make this goal achievable. The first step towards the goal is to demonstrate energizing a boundary layer by manipulating controlled, well-characterized, synthetically generated structures in well-coordinated boundary layer experiments and direct numerical simulations (DNS). The preliminary DNS successfully demonstrated optimization of control jet actuation using two different control methods, which deflected a prototypical LSM towards the surface. Preliminary work has created a suitable actuator based on a synthetic jet and demonstrated it in the lab. The specific tasks proposed in this collaborative 3-year project are: (1) develop and implement control algorithms to selectively move synthetically generated LSMs in matched experiments and DNS, (2) quantify the re-energization achieved by moving different kinds of LSMs to guide target prioritization, and (3) test and optimize the re-energization of a turbulent boundary layer with an eye toward separation control and wind power applications. The results of this project will be made publicly available through online platforms and enhanced classroom activity. The project will also help recruit graduate students from underrepresented groups and for several undergraduate research projects.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.