Aerodynamic Flow Control

Abstract

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.

Effects of Wall-Normal and Angular Momentum Injections in Airfoil Separation Control

“…We consider arrangements where swirl is introduced in a co-rotating (COR) or counter-rotating (CTR) manner. The magnitude of the wall-normal velocity is chosen such that the coefficient of momentum is on the same order of magnitude as in previous successful separation control studies [49]. Moreover, the magnitude of azimuthal velocity is selected such that the maximum velocity is on the same order of magnitude as the freestream, which can be regarded as the approximate upper bound for rotational motion induced by vortex generators.…”

Experimental method to quantify the efficiency of the first two operational stages of nanosecond dielectric barrier discharge plasma actuators

“…q=q o t ≤ n pulses f (3) q=0 t> n pulses f where f is the discharge frequency and n pulses is the number of pulses within a burst. In the current investigation, the discharge is modelled as a continuous and time-constant heat source ( q o ) acting over the given discharge time n pulses /f.…”

“…Unsteady flow control techniques [1] that use periodic excitations to manipulate flow stability [2,3] have the potential to overcome any other active flow control technique in terms of efficiency [4] because of the relatively low amount of energy they use. DBD (Dielectric Barrier Discharge) plasma actuators belong to this category.…”

Review of variable leading-edge patents for aircraft wings and engine inlets and their relevance for variable pitot inlets in future supersonic transport

“…The third basic approach for the implementation of variable pitot inlet cowls is the control of the flow boundary layer [130]. By avoiding flow separations, boundary layer control allows the use of slim geometries with low aerodynamic drag [131].…”