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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.


Papers
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R. Vepa1
01 Feb 1977
TL;DR: In this article, a general theory of finite state modeling of aerodynamic loads on thin airfoils and lifting surfaces performing completely arbitrary, small, time-dependent motions in an airstream is developed and presented.
Abstract: A general theory of finite state modeling of aerodynamic loads on thin airfoils and lifting surfaces performing completely arbitrary, small, time-dependent motions in an airstream is developed and presented. The nature of the behavior of the unsteady airloads in the frequency domain is explained, using as raw materials any of the unsteady linearized theories that have been mechanized for simple harmonic oscillations. Each desired aerodynamic transfer function is approximated by means of an appropriate Pade approximant, that is, a rational function of finite degree polynomials in the Laplace transform variable. The modeling technique is applied to several two dimensional and three dimensional airfoils. Circular, elliptic, rectangular and tapered planforms are considered as examples. Identical functions are also obtained for control surfaces for two and three dimensional airfoils.

112 citations

Journal ArticleDOI
TL;DR: In this paper, surface pressure distributions and wake profiles were obtained for a NACA0012 airfoil to determine the lift, drag, and pitching-moment coefficients for various configurations.
Abstract: Experimental measurements of surface pressure distributions and wake profiles were obtained for a NACA0012 airfoil to determine the lift, drag, and pitching-moment coefficients for various configurations. The addition of a Gurney flap increased the maximum lift coefficient from 1.37 to 1.74, however there was a drag increment at low-to-moderate lift coefficient. In addition, the boundary layer profile measurements were taken using a rake of total pressure probes at the 90% chord location on the suction side. The effective Gurney flap height is about 2% of chord length, which provides the highest lift-to-drag ratio among the investigated configurations when compared with the clean NACA0012 airfoil. In this case, the device remains within the boundary layer.

112 citations

Journal ArticleDOI
TL;DR: In this paper, the authors performed near-surface hot-wire experiments on an airfoil undergoing large-amplitude pitching motions about its quarter chord and showed the dramatic effect of pitch rate on flow structure.
Abstract: FLOW visualization and near-surface hot-wire experiments were performed in the U.S.A.F Academy Aeronautics Laboratory subsonic wind tunnel on an airfoil undergoing large-amplitude pitching motions about its quarter chord. The experiments were conducted using a NACA 0015 airfoil at an airfoil Reynolds number of 45,000. Two cases are presented in which the angular pitching rate a is maintained constant during the motion. These two cases represent two different nondimensional pitching rates a+, where ot+ is equal to 6; nondimensionalized by the chord c and the freestream velocity U^ (a + ^ac/U^). Data for the two cases where values of a+ are equal to 0.2 and 0.6 show the dramatic effect of pitch rate on flow structure. Largescale vortical structures are seen in both cases at high angles of attack but appear much later and are of a different form for the case with the larger a+ value. These structures are very energetic, producing reverse flow velocities near the airfoil surface of 1.0-2.1 times the freestream velocity.

112 citations

Journal ArticleDOI
TL;DR: In this article, a two-dimensional airfoil with a free-play nonlinearity in pitch subject to incompressibl e flow was analyzed and the aerodynamic forces were evaluated using Wagner's function and the resulting equations integrated numerically to give time histories of the air-foil motion.
Abstract: A two-dimensiona l airfoil with a free-play nonlinearity in pitch subject to incompressibl e flow has been analyzed. The aerodynamic forces on the airfoil were evaluated using Wagner's function and the resulting equations integrated numerically to give time histories of the airfoil motion. Regions of limit cycle oscillation are detected for velocities well below the linear flutter boundary, and the existence of these regions is strongly dependent on the initial conditions and properties of the airfoil. Furthermore, for small structural preloads, narrow regions of chaotic motion are obtained, as suggested by power spectral densities, phase-plane plots, and Poincare sections of the airfoil time histories. The existence of this chaotic motion is strongly dependent on a number of airfoil parameters, including, mass, frequency ratio, structural damping, and preload.

112 citations

Patent
29 May 2003
TL;DR: In this paper, first stage turbine buckets have airfoil profiles substantially in accordance with Cartesian coordinate values of X, Y and Z set forth Table I wherein X and Y values are in inches and Z values are non-dimensional values from 0 to 1 convertible to Z distances in inches by multiplying the Z values by the height of the airfoils in inches.
Abstract: First stage turbine buckets have airfoil profiles substantially in accordance with Cartesian coordinate values of X, Y and Z set forth Table I wherein X and Y values are in inches and the Z values are non-dimensional values from 0 to 1 convertible to Z distances in inches by multiplying the Z values by the height of the airfoil in inches. The X and Y values are distances which, when connected by smooth continuing arcs, define airfoil profile sections at each distance Z. The profile sections at each distance Z are joined smoothly to one another to form a complete airfoil shape. The X, Y and Z distances may be scalable as a function of the same constant or number to provide a scaled up or scaled down airfoil section for the bucket. The nominal airfoil given by the X, Y and Z distances lies within an envelop of ±0.055 inches in directions normal to the surface of the airfoil.

112 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,083
20221,871
2021923
2020979
20191,097
20181,002