ECN publicatie:
Application of a modified Theodorsen model to the estimation of aerodynamic forces and aeroelastic stability
Gepubliceerd door: Publicatie datum:
ECN Windenergie 1-11-2004
ECN publicatienummer: Publicatie type:
ECN-RX--04-120 Conferentiebijdrage
Aantal pagina's: Volledige tekst:
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Gepresenteerd op: European Wind Energy Conference 2004, London, UK, 22-25 november 2004.


Unsteady effects in attached flow are of importance for the damping of edge wise vibrations, also for pitch regulated wind turbines.

In a number of aeroelastic codes, these effects are treated with the classical Theodorsen model. This is the case when the Leishman Beddoes [1] model is used, in which the Theodorsen model is included. However, Theodorsen?s model is based on 2D flow. Although 2D flow is also the basis for profile aerodynamics on rotating blades in the BEM method, especially the shed wake part of the flow is definitely different in the rotating blade case. The difference between the 2D and the 3D rotating case was quantified in [2] as far as induced velocity is concerned. However in that paper, no link was made to unsteady aerodynamic forces. This part is fully  developed in the present paper. The expression for aerodynamic lift is cast in the form of so called quasi-steady lift force as often used in BEM modelling, plus and additional part that results from the present theory. Also, a unsteady drag force is identified and quantified.

Application of the theory to the aerodynamic damping of in-plane vibrations will be shown at the conference.


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