Development of Strategies for Flow Management and/or Re-arrangement

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Many industrial products contain flow systems whose performance affects the overall product capabilities, especially the energy cost of their operation. Reduction of the energy cost may come through the proper control/management/re-arrangement of flows within these systems. The present work is focused on the development of control techniques taking advantage of patterns of weak actuators which are individually irrelevant but can affect the flow in a decisive manner if arranged in spatial patterns. Since systems of actuators produce distributed forcing, identifying their most effective patterns and determining what can be achieved with these patterns are the goals of this work. Laminar, transitional as well as turbulent flows are targeted with priority given to passive techniques due to their simplicity and lack of failure-prone moving parts.*** The use of various physical phenomena capable of producing the desired distributed forcing will be considered. This includes the design of surface topography, determination of patterns of surface heating/cooling, investigation of patterns of surface transpiration as well as studies of patterns of surface vibrations. The forcing creates a direct flow response, i.e. spatial modulations, which may lead to the drag reduction by itself. The same forcing may create an indirect response where the flow modulations change the flow stability and the system bifurcates to a new state with a very minimal external actuation. It will be determined what can be achieved with both types of responses and under what conditions.*** The proposed work is divided into six themes. The first theme will determine the tolerance of the laminar-turbulent transition process to the presence of distributed surface. The second theme will identify surface topographies which can produce smaller friction drag in laminar as well as in turbulent flows. The third theme will identify surface topographies which both reduce frictional drag and control the laminar-turbulent transition. The fourth theme will use heating and corrugation patterns to control convective heat transfer with the more efficient heat exchangers being the goal. The fifth theme will look at the control of phase change processes using surface roughness and heating patterns with goals ranging from the control of airfoil icing to cooling of extremely hot surfaces. The sixth theme will determine how patterns of surface vibrations can be harnessed for drag reduction purposes and development of alternative propulsion schemes. Themes (a)-(c) will benefit the aerospace industry, resulting in the increase of its competitiveness. Themes (d)-(e) will benefit the energy and processing industries, potentially leading to the development of new products. Theme (e) will assist entities involved in the development of water crafts, removing some of the propulsion limiting factors.