Flow control and origins of turbulence

该项目的重点是发展战略的流动操纵/控制/重新安排使用分布式强迫。术语“分布式强迫”在这里表示在固体/流体界面处产生弱力的各种方法;这与局部施加的集中和/或强强迫相反。产生分布式强迫的方法可以依赖于使用表面粗糙度、微机电设备（MEMS）、壁蒸发、离子风效应、加热等，并且可以应用于层流、过渡流和湍流。弱分布强迫是感兴趣的，因为它的创建与较低的重量和较小的压力损失的惩罚相比，所需的强强迫。虽然强强迫总是被期望产生大的流量变化，弱强迫可能是有效的，只有当它有正确的空间/时间分布。预计，弱强迫可能会造成流量的变化，其模式的特征尺度的顺序，而不仅仅是其大小的顺序。为了有效，该策略必须利用各种流动不稳定性，这些流动不稳定性以自然的方式在不同模式之间重新分配总流动能量。如果控制/重新布置策略被适当地设计，则将仅需要小的外部能量输入来启动重新布置过程。初步结果表明，流系统的响应表现出一般的相似性，无论用于产生强迫的物理机制，只要强迫的空间分布是相似的，这一事实强调了所提出的方法的鲁棒性和广泛的适用性。该项目将探索的应用包括燃料电池微混合器的设计，微型热交换器，层流翼型，可能导致低阻力的表面纹理，湍流中大型结构的操纵技术，依赖于表面振动的推进装置和哮喘诊断程序等。

The project is focused on the development of strategies for flow manipulation/control/re-arrangements using distributed forcing. The term "distributed forcing" denotes here various methods of producing weak forces at the solid/fluid interface; this is opposite to the concentrated and/or strong forcing applied locally. Methods of generating distributed forcing may rely on the use of surface roughness, micro-electro-mechanical devices (MEMS), wall transpiration, ionic wind effect, heating, etc., and can be applied to laminar, transitional and turbulent flows. Weak distributed forcing is of interest because its creation is associated with lower weight and smaller pressure loss penalty as compared with that required by a strong forcing. While strong forcing is always expected to produce large changes in the flow, a weak forcing may be effective only if it has correct spatial/temporal distribution. It is expected that weak forcing may create changes in the flow of the order of the characteristic scale of its pattern rather than just of the order of its magnitude. This strategy, in order to be effective, must take advantage of various flow instabilities, which re-distribute in a natural way the total flow energy among different modes. Only a small external energy input will be required in order to initiate the re-arrangement process if the control/re-arrangement strategy is properly designed. Preliminary results show that responses of flow systems show generic similarities regardless of the physical mechanisms used to generate forcing as long as the spatial distribution of forcing is similar; this fact underlines the robustness of the proposed approach and its wide range of applicability. Applications to be explored in this project include design of micro-mixers for fuel cells, micro-heat exchangers, laminar airfoils, surface textures that could lead to lower drag, techniques for manipulation of large structures in turbulent flows, propulsive devices relying on surface vibrations and asthma diagnosis procedures, among many others.