Aerodynamic Flow Control

Active flow control (AFC) has re-emerged as a formidable research area in aerodynamics; this chapter provides a broad overview of modern developments. The control of large coherent structures via periodic perturbations and the mechanical means to achieve this have been at the heart of these developments. AFC has been demonstrated in wind tunnels over a 4 order-of-magnitude Reynolds number range and at high subsonic Mach numbers. Recently, an active flow control system for tiltrotor download alleviation was successfully flight tested. Most of the AFC research has focused on airfoil configurations including so-called simplified high-lift systems, although drag reduction, three-dimensional configurations and flows, are also actively researched. Experiments that elucidate new aspects or isolate controlling parameters are considered to be invaluable for advances in the foreseeable future. Concurrently, the development of effective, robust, and system-efficient actuators and sensors will determine the scope of applications. Computational fluid dynamics (CFD), with various levels of turbulence model complexity, is the primary tool for prediction of these flows. Coordinated experiments designed specifically for CFD validation will be invaluable for developing these codes. Recent progress in the arena of simulation methods such as direct numerical simulation (DNS), large eddy simulation (LES), and hybrid Reynolds-averaged Navier–Stokes (RANS)/LES is expected to continue. Nevertheless, due to the expense of these methods, effort should also be expended in improving RANS predictions.