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.

Oscillating Airfoils at High Mach Number

Abstract: A simple formula is given for the pressure distribution on an oscillating airfoil in two-dimensional flow at high Mach Number. The formula is expected to be reasonably accurate if the pressure on the surface remains within the range 0.2 to 3.5 times the mainstream pressure. To illustrate the application of the formula, some results for symmetrical airfoils performing pitching oscillations are obtained and compared with results obtained from existing theories in the case of high Mach Number.

Aspects of low- and high-frequency actuation for aerodynamic flow control

Abstract: Control approaches for separated flows over aerodynamic (or bluff) bodies in which the separated flow domain scales with the characteristic length of the body are distinguished by the frequency band of the actuation input. In an approach that relies on the narrowband receptivity of the separating shear layer that is coupled to the wake (shedding) instability and scales with the characteristic advection time over the separated domain, aerodynamic performance is partially restored by a Coanda-like deflection of the forced separating shear layer toward the surface. Because the instability of the unforced shear layer may already be driven by global vortex shedding, the advection of the vortices of the forced (or controlled) layer along the surface and their ultimate shedding into the near wake can couple to wake instabilities and, therefore, may result in unsteady aerodynamic forces in the controlled flow. A different control strategy that emphasizes full or partial suppression of separation by fluidic modification of the apparent aerodynamic shape of the surface relies on controlled interaction between the actuator and the crossflow on a scale that is at least an order of magnitude smaller than the relevant global length scales.

Visualization by PIV of dynamic stall on a vertical axis wind turbine

Abstract: The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle θ of the blade’s sections’ angle of attack, perceived velocity and Reynolds number. The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it, and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/circulation distribution are presented), in terms of the phase locked average and the random component.

Nonlinear Inviscid Aerodynamic Effects on Transonic Divergence, Flutter, and Limit-Cycle Oscillations

Abstract: By the use of a state-of-the-art computational e uid dynamic (CFD) method to model nonlinear steady and unsteady transonice owsin conjunction with a linearstructural model,an investigationismadeinto how nonlinear aerodynamics can effect the divergence, e utter, and limit-cycle oscillation (LCO) characteristics of a transonic airfoil cone guration. A single-degree-of-freedom (DOF) model is studied for divergence, and one- and two-DOF models are studied for e utter and LCO. A harmonicbalancemethod in conjunction with the CFD solver is used to determine the aerodynamics for e nite amplitude unsteady excitations of a prescribed frequency. A procedure for determining the LCO solution is also presented. For the cone guration investigated, nonlinear aerodynamic effects are found to produce a favorable transonic divergence trend and unstable and stable LCO solutions, respectively, for the one- and two-DOF e utter models. Nomenclature a = nondimensional location of airfoil elastic axis, e=b b, c = semichord and chord, respectively cl, cm = coefe cients of lift and moment about elastic axis, respectively e = location of airfoil elastic axis, measured positive aft of airfoil midchord h, ® = airfoil plunge and pitch degrees of freedom I® = second moment of inertia of airfoil about elastic axis

Analysis of the development of dynamic stall based on oscillating airfoil experiments

Abstract: The effects of dynamic stall on airfoils oscillating in pitch were investigated by experimentally determining the viscous and inviscid characteristics of the airflow on the NACA 0012 airfoil and on several leading-edge modifications. The test parameters included a wide range of frequencies, Reynolds numbers, and amplitudes-of-oscillation. Three distinct types of separation development were observed within the boundary layer, each leading to classical dynamic stall. The NACA 0012 airfoil is shown to stall by the mechanism of abrupt turbulent leading-edge separation. A detailed step-by-step analysis of the events leading to dynamic stall, and of the results of the stall process, is presented for each of these three types of stall. Techniques for flow analysis in the dynamic stall environment are discussed. A method is presented that reduces most of the oscillating airfoil normal force and pitching-moment data to a single curve, independent of frequency or Reynolds number.