The recent introduction of ever larger wind turbines poses new challenges with regard to understanding the mechanisms of unsteady flow-structure interaction. An important aspect of the problem is the aeroelastic stability of the wind turbine blades, especially in the case of combined flap/lead-lag vibrations in the stall regime. Given the limited experimental information available in this field, the use of CFD techniques and state-of-the-art viscous flow solvers provides an invaluable alternative towards the identification of the underlying physics and the development and validation of sound engineering-type aeroelastic models. Navier-Stokes-based aeroelastic stability analysis of individual blade sections subjected to combined pitch/flap or flap/lead-lag motion has been attempted by the present consortium in the framework of the concluded VISCEL JOR3-CT98-0208 Joule III project.A 2D simplified investigation of the classical flutter problem is based on the stability analysis of the so-called typical (blade) section. The latter is hinged in such a way that its motion has two independent degrees of
Aerodynamic modelling of HAWT rotors by means of ''engineering methods'' has reached a saddle point, where no further development can be expected without a breakthrough in understanding the physics of unsteady, rotating three-dimensional flows. However, such a breakthrough becomes ever more necessary, as the size of the wind turbines increases. With the experimental work in that direction being mostly limited to observing the phenomena and interpreting the associated mechanisms, and its increased cost, alternatives are being sought. The use of CFD techniques and state-of-the-art Navier-Stokes solvers is considered a very serious contender, a belief shared by the members of the present consortium, which has worked on the VISCEL JOR3-CT98-0208 Joule III project. This project's goal was to determine the aerodynamic characteristics as well as the aeroelastic behaviour of wind turbine blades across their broad range of operational conditions, from attached to highly separated flow regimes. The work programme included specific tasks for the validation and assessment of existing 3D solvers, for the parametric study of 3D flow around realistic blades and for the investigation of aeroelastic stability, at the blade section level.
This paper describes the research activities conducted hy the European Research consortium HELIFUSE during the first vear of this Brite-EuRaM uroiect. The work consisted of Navier-Stokes comnutatinns on nre-selected test cases taken . " out of a n extensive wind tunnel test program a t the ONERA F l wind tunnel. The calculations were performed by three national research institutes (CIRA, DLR, ONERA), three helicopter manufacturers (Agusta, Eurocopter, GKN-Westland), one software company (Sirnulog) and two universities (DTU, IAG). The aim of the work was to simulate the complex Rowfield around the fuselage of the wind tunnel tests. Rlind test calculations and wind tunnel data were in very good agreement for the surface pressure distribution, hut showed some discrepancies in the drag prediction accuracy. I n order to understand the reasons for this scatter, two additional computational tests were performed: 1) computation of a fuselage test case with one Navier-Stokes code on all the different structured grids; 2) computations by all the structured Navier-Stokes codes on one common grid. These results have reduced the large scatter in the drag data from CFD analysis, although some discrepancy still exists.
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