Smart skin for control of wall-bounded turbulent flows

边界层是固体表面附近的一层薄薄的流体，其中流体速度从固体表面的速度转变为整体流体速度。流体中的剪切应力产生了这种速度梯度，并以表面摩擦的形式投射到表面上。在大多数工业情况下，例如，飞机上的流动或管道内的流动，边界层中流体元素的运动是混沌的。这样的流体层被称为湍流边界层（TBL），它具有较大的速度梯度，从而产生较大的表面摩擦。此外，当压力梯度增加到TBL上时，如在扩散器或飞机机翼上，TBL可能会从表面分离。这就产生了压力阻力和强烈的流体-结构相互作用。因此，TBL是飞机、潜水器、船舶和管道中高燃料消耗、污染和结构振动的主要来源。由于这一整体效应，在管制有毒物质方面的任何进展，都将对我们的社会经济和环境保护需要产生深远的影响。

A boundary layer is a thin layer of fluid in the immediate vicinity of a solid surface where fluid velocity transitions from the velocity of the solid surface to the bulk fluid velocity. The shear stress in the fluid generates this velocity gradient, and projects as skin-friction' on the surface. In most industrial situations, for example, the flow over an aircraft or inside a pipeline, the motions of fluid elements in the boundary layer are chaotic. Such a fluid layer is known as a turbulent boundary layer (TBL), and has a larger velocity gradient that generates greater skin-friction. In addition, when an increasing pressure gradient is imposed on a TBL, like in a diffuser or on an aircraft wing, the TBL may separate from the surface. This generates pressure drag' and strong fluid-structure interactions. As a result, the TBL is the chief source of high fuel consumption, pollution, and structural vibration in aircrafts, submersibles, ships, and pipelines. Due to this integral effect, any progress in the control of TBLs will have a profound impact on our socio-economic and environmental protection needs. The subject of this research program is the control of attached and separated TBLs using a novel smart skin'. To achieve this goal, we will first experimentally characterize the surface pressure of large-scale motions in attached and separated TBLs to develop a predictive model for turbulence control. In parallel, we will develop deformable surfaces that can generate on-demand local surface depression or protrusion. Linear actuators, with a frequency and displacement that matches the pressure footprint, will be integrated under a deformable skin. We will implement an array of active deformable panels and surface pressure sensors into a smart skin'. Finally, the performance of the smart skin' will be evaluated in a closed-loop system for active control of attached and separated TBLs. In the long-term, the proposed program will increase our fundamental knowledge of coherent motions in TBLs and provide guidelines on how to control TBLs. The developed smart skin' will make it possible to manipulate a variety of turbulent flows including TBLs. The smart skin will also become a test-bench for the application of advanced control algorithms, artificial intelligence, and machine learning. Such an approach can ultimately modernize how we handle turbulence. It can make a breakthrough by bringing turbulence control to a variety of industrial sectors to increase efficiency and reduce environmental footprints. In addition, the multidisciplinary nature of this research program will train highly qualified personnel who are trained in a variety of disciplines.