Airfoil

About: Airfoil is a research topic. Over the lifetime, 24696 publications have been published within this topic receiving 337709 citations. The topic is also known as: aerofoil & wing section.

Low-speed single-element airfoil synthesis

Abstract: Large quantities of experimental data exist on the characteristics of airfoils operating in the Reynolds number range between one and ten million, typical of conventional atmospheric wind tunnel operating conditions. Beyond either end of this range, however, good experienental data becomes scarce. Designers of model airplanes, hang gliders, ultralarge energy efficient transport aircraft, and bio-aerodynamicists attempting to evaluate the performance of natural flying devices, are hard pressed to make the kinds of quality performance/design estimates taken for granted by sailplane and general aviation aerodynamicists. Even within the usual range of wind tunnel Reynolds number, much of the data is for "smooth" models which give little indication of how a section will perform on a wing of practical construction. The purpose of this paper is to demonstrate the use of recently developed airfoil analysis/design computational tools to clarify, enrich and extend the existing experimental data base on 1ow-speed, single element airfoils, and then proceed to a discussion of the problem of tailoring an airfoil for a specific application at its appropriate Reynolds number. This latter problem is approached by use of inverse (or "synthesis") techniques, wherein a desirable set of boundary layer characteristics, performance objectives, and constraints are specified, which then leads to derivation of a corresponding viscous flow pressure distribution. In this plocedure, the airfoil shape required to produce the desired flow characteristics is only extracted towards the end of the design cycle. This synthesis process is contrasted with the traditional "analysis" (either experimental or computational) approach in which an initial profile shape is selected which then yields a pressure distribution and boundary layer characteristic, and finally some perfonnance level. The final configuration which provides the required performance is derived by cut-and-try adjustments to the shape. These two approaches are shown disgramatically.

Effects of Dynamic Stall on Propulsive Efficiency and Thrust of Flapping Airfoil

Abstract: Numerical simulations of dynamic stall phenomena around an airfoil oscillating in a coupled mode, in which the pitching and heaving oscillations have some phase difference, have been performed with a Navier ‐Stokes code. The propulsive efe ciency and the thrust have been calculated for various combinations of the phase difference and the reduced frequency for two different amplitude ratios. The effects of the dynamic stall phenomena on the behaviors of the propulsive efe ciency and thrust are discussed in detail by examination of each e ow pattern obtained. Highest efe ciency has been observed for the case in which the pitching oscillation advances 90 deg ahead of the heaving oscillation and the reduced frequency is at some optimum value, for which there appears no appreciable e ow separation in spite of large-amplitude oscillations. For phase angles and reduced frequency other than thisbestcondition, efe ciency israpidly degraded by theoccurrenceof thelarge-scaleleading-edgeseparation.

Dynamic stall experiments on the NACA 0012 airfoil

Abstract: The flow over a NACA 0012 airfoil undergoing large oscillations in pitch was experimentally studied at a Reynolds number of and over a range of frequencies and amplitudes. Hot-wire probes and surface-pressure transducers were used to clarify the role of the laminar separation bubble, to delineate the growth and shedding of the stall vortex, and to quantify the resultant aerodynamic loads. In addition to the pressure distributions and normal force and pitching moment data that have often been obtained in previous investigations, estimates of the unsteady drag force during dynamic stall have been derived from the surface pressure measurements. Special characteristics of the pressure response, which are symptomatic of the occurrence and relative severity of moment stall, have also been examined.