Unsteady aerodynamic modeling for arbitrary motions

Edwards, John W.; Ashley, Holt; Breakwell, J. V.

doi:10.2514/3.7348

Cited by 177 publications

(72 citation statements)

References 8 publications

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“…(10) can be extended to moderately separated flows by defining the limits δ and δ − in the integral of the vorticity field [Eq. (8)] as the sufficiently large distances from the airfoil surface beyond the viscous flow region. In this sense, the whole separated flow plus an airfoil is vertically compressed into a vortex sheet with the strength γx; t. When γx; t is calculated from the vorticity fields obtained from global velocity measurements and CFD, the nonlinear effects associated with viscous separated flows could be naturally incorporated in the TALF particularly in the vortex lift.…”

Section: Thin-airfoil Lift Formulamentioning

confidence: 99%

“…The pioneering studies on unsteady thin-airfoil theory were conducted by Wagner [3], Küssner [4], Theodorsen [5], and von Kármán and Sears [6]. Recently, because of the renewed interests in active flutter control and flapping flight, considerable efforts have been made to apply thin-airfoil theory to unsteady flows associated with aeroelastic, flapping, and flexible wings [7][8][9][10][11][12][13]. The formulation given by von Kármán and Sears [6] based on the application of the vortex impulse is particularly insightful because the unsteady lift is explicitly expressed as a sum of the quasi-steady Kutta-Joukowski lift, the added-mass lift, and the wake-induced contribution.…”

mentioning

confidence: 99%

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Unsteady Thin-Airfoil Theory Revisited: Application of a Simple Lift Formula

et al. 2015

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The physical foundations of unsteady thin-airfoil theory are explored in the general framework of viscous flows. The thin-airfoil lift formula is derived by using the simple lift formula that contains the vortex lift and the lift associated with the fluid acceleration. From a broader perspective, the thin-airfoil lift formula could be applicable even when the flow around an airfoil is moderately separated, from which the classical von Kármán-Sears lift formula can be recovered as a reduced case. The quantitative relationship between boundary layer and lift generation is discussed. Direct numerical simulations of low-Reynolds-number flows over a flapping flat-plate airfoil are conducted to examine the accuracy and limitations of the thin-airfoil lift formula.

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Section: Thin-airfoil Lift Formulamentioning

confidence: 99%

mentioning

confidence: 99%

Unsteady Thin-Airfoil Theory Revisited: Application of a Simple Lift Formula

et al. 2015

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“…Using the Pade approximation to transform the integral form into a second order ordinary differential equation [9], we write…”

Section: Duhamel Formulationmentioning

confidence: 99%

“…On the other hand, to consider the effects of the wake dynamics of the airfoil, the augmented state variables are related to the other system parameters through the following differential equation [9]…”

Section: Duhamel Formulationmentioning

confidence: 99%

Experimental Identification of Concentrated Nonlinearity in Aeroelastic System

Abdelkefi

Vasconcellos

Hajj

et al. 2012

MATEC Web of Conferences

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Abstract. Identification of concentrated nonlinearity in the torsional spring of an aeroelastic system is performed. This system consists of a rigid airfoil that is supported by a linear spring in the plunge motion and a nonlinear spring in the pitch motion. Quadratic and cubic nonlinearities in the pitch moment are introduced to model the concentrated nonlinearity. The representation of the aerodynamic loads by the Duhamel formulation yielded accurate values for the flutter speed and frequency. The results show that the use of the Duhamel formulation to represent the aerodynamic loads yields excellent agreement between the experimental data and the numerical predictions.

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“…More recently there has been renewed interest centered on using approximations of Wagner and Theodorsen functions. In particular, Edwards et al (1979) derived generalized Theodorsen functions relating motions of the circulatory part of the airloads to the motion of the airfoil and applied it to subcritical and supercritical flutter conditions. Peters (2008) gives additional information on several finite-state models predicting forces and moments in the frequency domain, although one major drawback of these methods is that they cannot be integrated into a fully coupled simulation of the fluid-structure interaction.…”

Section: Iv11 Introductionmentioning

confidence: 99%