Multiscale Active Flow Control

Abstract

The physics of the multiscale patterns of flows is introduced in the first part: it is the foundation for analysis of the control of flow. Then a careful distinction is made between control as a passive mean for improving the properties of natural flows relevant to a given application, and control as a robust active tool to optimize a cost function. Improvements of the performances of engineering systems relying on flow of fluids may use passive means or active controller, sensors and actuators to withstand the external perturbations. Consideration of such types of active and passive control and of calming or increasing unsteadiness forms the subject matter of the following parts in flows of high Reynolds number relevant to major applications with turbulence or chaotic behavior. These progress towards increasing complexity of control: from the simpler control of amplitude of turbulence and chaos everywhere in the flow to achieve its homogenization to the more complex control aimed to reduce such amplitude. Methodology relying on a mix of experimental and numerical assessment of the problems and of possible solutions is needed for mastering the level of difficulties involved in complex flow control. The final part is devoted to the problems of applications, when a real-life controlled flow system is to be built, demonstrated and certified at the level of safety presently required for advanced aviation systems in operation.