Flow sensing, estimation and control in turbulent flows

湍流是人类能量消耗的重要组成部分，例如，在燃料中克服车辆的阻力或将流体从一个地方泵到另一个地方所需的电力。现在人们认识到，在看似随机的湍流中存在着有组织的运动;这些有组织的运动或相干结构对许多工程上感兴趣的量是至关重要的，如传热、阻力或噪声产生。目前的研究计划旨在提高我们对如何操纵这些相干结构的理解，以产生有用的工程结果，如增强传热，减少车辆阻力或减少噪音排放。建议的研究计划的目的是提高我们的知识，如何操纵相干结构的两个流，三维壁射流和流动后向台阶。当射流切向地指向表面时，形成三维壁射流。三维壁射流经常出现在加热和冷却应用、燃烧器、通风应用以及涂覆工艺中。三维壁射流强烈地“粘”在表面上，这导致射流沿壁横向向外沿着扩展和增长，比垂直于壁扩展和增长大5倍。我以前的大部分研究工作都是为了了解壁射流中的湍流相干结构是如何导致这种行为的。 所提出的研究的目标之一是修改壁射流中的相干结构，从而改变流动的表面覆盖。增强的表面覆盖在许多加热和冷却应用中将是有益的，并且可以用于防止流动分离和增加飞机机翼上的升力（因为更好地“粘”到表面的射流将不太容易分离）。另一方面，减少的表面覆盖率在需要更高水平的混合的通风和燃烧应用中将是有用的。 后向台阶上的流动是发展流动控制技术的第二个目标。后向台阶流动是车辆尾部经常出现的流动分离过程的简化模型。能够控制气流分离将减少车辆的阻力，从而提高燃油经济性并减少有害排放。由于气流分离过程产生的湍流是车辆内的噪声源，因此控制气流分离也将产生更安静的车辆。拟议的研究将努力实现分离控制的目标，首先开发工具，估计瞬时湍流速度场使用壁基传感器。

Turbulence is responsible for a significant portion of human energy consumption, for example, in fuel to overcome the drag on vehicles or the electricity required to pump fluids from place to place. It is now recognized that there are organized motions in seemingly random turbulent flows; these organized motions, or coherent structures, are critical to many quantities of engineering interest, like heat-transfer, drag, or noise production. The present research program aims to improve our understanding of how to manipulate these coherent structures to produce useful engineering results like enhanced heat-transfer, drag-reduction on vehicles, or reduced noise emissions. The proposed research program aims to improve our knowledge of how to manipulate the coherent structures in two flows, the three-dimensional wall jet and the flow over a backwards facing step. Whenever a jet is directed tangentially at a surface, a three-dimensional wall jet is formed. Three-dimensional wall jets occur frequently in heating and cooling applications, combustors, ventilation applications, as well as in coating processes. The three-dimensional wall jet strongly “sticks” to surfaces which causes the jet to spread and grow laterally outward along the wall 5 times greater than it grows perpendicular to the wall. Much of my previous research effort has gone into understanding how the turbulent coherent structures in the wall jet cause this behaviour. One of the goals of the proposed research is modifying the coherent structures in the wall jet so as to alter the surface coverage of the flow. Enhanced surface coverage would be beneficial in numerous heating and cooling applications and could be used to prevent flow separation and augment lift on aircraft wings (as a jet that “sticks” better to surfaces would be less prone to separate). Reduced surface coverage, on the other hand, would be useful in ventilation and combustion applications where higher levels of mixing are desired. The flow over a backwards facing step is the second flow targeted for developing flow control techniques. The flow over a backwards facing step is a simplified model of the flow separation process which occurs frequently on the rear of vehicles. Being able to control flow separation will reduce the drag on vehicles, thereby increasing fuel economy and reducing harmful emissions. As the turbulence created by flow separation processes is a source of noise within the vehicle, controlling flow separation will also create quieter vehicles. The proposed research will work towards the goal of separation control by first developing tools to estimate the instantaneous turbulent velocity field using wall based sensors.