Unsteady Aerodynamics of Multiple Airfoils in Configuration
27 Jun 2011-
TL;DR: In this paper, a potential flow model is used to study the unsteady flow past two airfoils in configuration, each of which is suddenly set into motion, and the airfoil bound vortices are modeled using lumped vortex elements.
Abstract: A potential flow model is used to study the unsteady flow past two airfoils in configuration, each of which is suddenly set into motion. The airfoil bound vortices are modeled using lumped vortex elements and the wake behind the airfoil is modeled by discrete vortices. This consists of solving a steady state flow problem at each time-step where unsteadiness is incorporated through the “zero normal flow on a solid surface” boundary condition at every time instant. Additionally, along with the “zero normal flow on a solid surface” boundary condition Kelvin’s condition is used to compute the strength of the latest wake vortex shed from the trailing edge of the airfoil. Location of the wake vortices is updated at each time-step to get the wake shape at each time instant. Results are presented to show the effect of airfoil-airfoil interaction and airfoil-wake interaction on the aerodynamic characteristics of each airfoil.
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07 Jan 2013
TL;DR: In this paper, a lumped vortex model coupled with vortex dissipation and vortex core criteria is used to study the unsteady flow past tandem pitching airfoils, which is solved using a combined zero-normal flow boundary condition and Kelvin condition.
Abstract: A lumped vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past tandem pitching airfoils. The unsteady wakes of both airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled flow is solved using a combined “zero-normal flow” boundary condition and Kelvin condition which results in (2N+2)X(2N+2) equations. Commercial software FLUENT is also used to study the flow tandem pitching airfoils. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the tandem airfoils pitching in or out of phase and also when only the leading airfoil pitches and the trailing airfoil is stationary.
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05 Feb 2001
TL;DR: In this article, a modern treatment of the subject, both the theory of inviscid, incompressible, and irrotational aerodynamics and the computational techniques now available to solve complex problems is presented.
Abstract: Low-speed aerodynamics is important in the design and operation of aircraft flying at low Mach number, and ground and marine vehicles. This 2001 book offers a modern treatment of the subject, both the theory of inviscid, incompressible, and irrotational aerodynamics and the computational techniques now available to solve complex problems. A unique feature of the text is that the computational approach (from a single vortex element to a three-dimensional panel formulation) is interwoven throughout. Thus, the reader can learn about classical methods of the past, while also learning how to use numerical methods to solve real-world aerodynamic problems. This second edition has a new chapter on the laminar boundary layer (emphasis on the viscous-inviscid coupling), the latest versions of computational techniques, and additional coverage of interaction problems. It includes a systematic treatment of two-dimensional panel methods and a detailed presentation of computational techniques for three-dimensional and unsteady flows. With extensive illustrations and examples, this book will be useful for senior and beginning graduate-level courses, as well as a helpful reference tool for practising engineers.
1,810 citations
743 citations
TL;DR: In this paper, the scaling laws and unsteady flow regime constraining both biological and man-made fliers have been reviewed and an explanation for aerodynamic gains seen in flexible versus rigid membrane wings, derived from a three-dimensional computational fluid dynamics model with an integrated distributed control algorithm, is presented.
412 citations
TL;DR: In this article, the authors investigated the resistance of a flat plate to the general flow, in terms of the dimensions of the vortex system at some distance behind the plate and the rate at which vorticity is leaving the edges of the plate.
Abstract: The general form of the flow behind an infinitely long thin flat plate inclined at a large angle to a fluid stream of infinite extent has been known for many years past. The essential features of the motion are illustrated in the smoke photograph given in fig. 1, Plate 6. At the edges, thin bands of vorticity are generated, which separate the freely-moving fluid from the “dead-water” region at the back of the plate; and at some distance behind, these vortex bands on account of their lack of stability roll up and form what is now commonly known as a vortex street (see fig. 2). Various theories for calculating the resistance of the plate have also been advanced from time to time. One of the earliest is the theory of “discontinuous” motion due to Kirchhoff and Rayleigh, who obtained the expression π sin α/4 + π sin α ρV2 b (see symbols) for the normal force per unit length of the plate. More recently Karman has obtained a formula for the resistance of a plate normal to the general flow, in terms of the dimensions of the vortex system at some distance behind the plate. In spite, however, of these and other important investigations, much more remains to be discovered before it can be said that the phenomenon of the flow is completely understood. No attempt has hitherto been made, as far as the writers are aware, to determine experimentally, at incidences below 90°, the frequency and speed with which the vortices pass downstream; the dimensions of the vortex system; the average strength of the individual vortices; or the rate at which vorticity is leaving the edges of the plate. The present investigation has been undertaken to furnish information on these features of the flow.
382 citations
TL;DR: In this article, the point vortex approximation of a vortex sheet in two dimensions is examined and a remedy for some of its shortcomings is suggested. The approximation is then applied to the study of the roll-up of the vortex sheet induced by an elliptically loaded wing.
265 citations