Flow Control: The Future

The subject of e ow control, particularly reactive e ow control, is broadly introduced, leaving some of the details to other papers in this special volume of the Journal of Aircraft . The ability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance. In general, methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence augmentation, and noise suppression are sought for both wall-bounded and free-shear e ows. An attempt is made to present a unie ed view of the means by which different methods of control achieve a variety of end results. The important advances in the e eld of e ow control that took place during the past few years are discussed. Spurred by the recent developments in chaos control, microfabrication and neural networks, reactive control of turbulent e ows is now in the realm of the possible for future practical devices. HEability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance, and this undoubtedly accounts for the subject being more hotly pursuedbyscientistsandengineersthananyothertopicine uidmechanics.The potential benee ts of realizingefe cient e ow-controlsystems range from saving billions of dollars in annual fuel costs for land, air,and seavehiclesto achieving economically andenvironmentally more competitive industrial processes involving e uid e ows. Methodsofcontroltoeffecttransitiondelay,separationpostponement,lift enhanc...