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.

NREL airfoil families for HAWTs

Abstract: The development of special-purpose airfoils for horizontal-axis wind turbines (HAWTs) began in 1984 as a joint effort between the National Renewable Energy Laboratory (NREL), formerly the Solar Energy Research Institute (SERI), and Airfoils, Incorporated. Since that time seven airfoil families have been designed for various size rotors using the Eppler Airfoil Design and Analysis Code. A general performance requirement of the new airfoil families is that they exhibit a maximum lift coefficient (c{sub l,max}) which is relatively insensitive to roughness effects. The airfoil families address the needs of stall-regulated, variable-pitch, and variable-rpm wind turbines. For stall-regulated rotors, better peak-power control is achieved through the design of tip airfoils that restrain the maximum lift coefficient. Restrained maximum lift coefficient allows the use of more swept disc area for a given generator size. Also, for stall-regulated rotors, tip airfoils with high thickness are used to accommodate overspeed control devices. For variable-pitch and variable-rpm rotors, tip airfoils having a high maximum lift coefficient lend themselves to lightweight blades with low solidity. Tip airfoils having low thickness result in less drag for blades having full-span pitch control. Annual energy improvements from the NREL airfoil families are projected to be 23% to 35% for stall-regulatedmore » turbines, 8% to 20% for variable-pitch turbines, and 8% to 10% for variable-rpm turbines. The improvement for stall-regulated turbines has been verified in field tests.« less

Optimization of the Aerodynamic Plasma Actuator as an Electrohydrodynamic (EHD) Electrical Device

Abstract: Electrohydrodynamic plasma actuators have proven effective for flow attachment in internal and external aerodynamics, and for modification of the lift, drag, and stall angle of airfoils. The performance of plasma actuators has been studied with such classical aerodynamic tools as wind tunnels, drag balances, Pitot tubes, smoke flow visualization, and fluid dynamic modeling programs. However, the physical processes and power flows that occur in plasma actuators, before the plasma ions transfer their momentum to the neutral background gas, are those of an electrical device. Optimization of such actuators needs to include the methods of electrical engineering and plasma physics, including classical electrical discharge physics. To implement a program of optimization, we have conceptually divided the power flow through a plasma actuator into the following four sinks: 1.) Reactive power losses due to inadequate impedance matching of the power supply to the actuator; 2.) Dielectric heating of the actuator insulating materials; 3.) Power required to maintain the atmospheric pressure plasma; and 4.) Power coupled to the neutral gas flow by ion-neutral collisions. These four power flows can be, and usually are, of comparable magnitude. In this paper, we review our progress in understanding and minimizing the first three power flows, and maximizing the fourth by adjustment of the actuator geometry and materials, as well as such plasma parameters as the RF frequency and RMS voltage.

Wall interference in a two-dimensional-flow wind tunnel, with consideration of the effect of compressibility

Abstract: Theoretical tunnel-wall corrections are derived for an airfoil of finite thickness and camber in a two-dimensional-flow wind tunnel. The theory takes account of the effects of the wake of the airfoil and of the compressibility of the fluid, and is based upon the assumption that the chord of the airfoil is small in comparison with the height of the tunnel. Consideration is given to the phenomenon of choking at high speeds and its relation to the tunnel-wall corrections. The theoretical results are compared with the small amount of low-speed experimental data available and the agreement is seen to be satisfactory, even for relatively large values of the chord-height ratio.

Flying-Hot-wire Study of Flow Past an NACA 4412 Airfoil at Maximum Lift

Abstract: Hot-wire measurements have been made in the boundary layer, the separated region, and the near wake for flow past an NACA 4412 airfoil at mad mum lift. The Reynolds number based on chord was about 1,500,000. Special care was taken to achieve a two-dimensional mean flow. The main instrumentation was a flying hot wire; that is, a hot-wire probe mounted on the end of a rotating arm. The probe velocity was sufficiently high to avoid the usual rectification problem by keeping the relative flow direction always within a range of ± 30 deg from the probe ads. A digital computer was used to control synchronized sampling of hot-wire data at closely spaced points along the probe arc. Ensembles of data were obtained at several thousand locations in the flowfield. The data include Intermittency, two components of mean velocity, and twelve mean values for double, triple, and quadruple products of two velocity fluctuations. No Information was obtained about the third (spanwise) velocity component. An unexpected effect of rotor interference was identified and brought under reasonable control. The data are available on punched cards in raw form and also after use of smoothing and interpolation routines to obtain values on a fine rectangular grid aligned with the airfoil chord. The data are displayed In the paper as contour plots.

Finite state induced flow models. II - Three-dimensional rotor disk

Abstract: In Part I of this two-part article, we developed a finite state induced flow model for a two-dimensional airfoil. In this second part, we develop a finite state induced flow model for the three-dimensional induced flow for a rotor. The coefficients of this model are found in a compact closed form. Although the model does not presuppose anything about the source of lift on the rotating blades, applications are given in which the Prandtl assumption is invoked. That is, the two-dimensional lift equations are used at each radial station, but with the inflow from the three-dimensional model. The results are shown to reduce (in several special cases) to Prandtl-Golds tein theory, Theodorsen theory, Loewy theory, dynamic inflow, and blade-element momentum theory. Comparisons with vortex-filament models and with experimental data in hover and forward flight also show excellent correlation.