Flow control and origins of turbulence

点击翻译按钮获取中文摘要

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.