Abstract
Abstract. In this paper, a method to determine the angle of attack on a wind turbine rotor blade using a chordwise pressure distribution measurement was applied. The approach used a reduced number of pressure tap data located close to the blade leading edge. The results were compared with the measurements from three external probes mounted on the blade at different radial positions and with analytical calculations. Both experimental approaches used in this study are based on the 2-D flow assumption; the pressure tap method is an application of the thin airfoil theory, while the probe method applies geometrical and induction corrections to the measurement data. The experiments were conducted in the wind tunnel at the Hermann Föttinger Institut of the Technische Universität Berlin. The research turbine is a three-bladed upwind horizontal axis wind turbine model with a rotor diameter of 3 m. The measurements were carried out at rated conditions with a tip speed ratio of 4.35, and different yaw and pitch angles were tested in order to compare the approaches over a wide range of conditions. Results show that the pressure tap method is suitable and provides a similar angle of attack to the external probe measurements as well as the analytical calculations. This is a significant step for the experimental determination of the local angle of attack, as it eliminates the need for external probes, which affect the flow over the blade and require additional calibration.
Highlights
The angle of attack (AoA) is, by definition, a 2-D concept
The AoA estimation based on the surface pressure measurements depends on the relative dynamic pressure and the pressure difference ( P (12.5%c)); see Eq (6)
A method to determine the AoA based on the pressure difference between the pressure and suction side on a wind turbine blade was tested
Summary
The angle of attack (AoA) is, by definition, a 2-D concept. on a wind turbine, the rotating system, i.e., a blade, is under 3-D effects such as tip and root vortices, yaw misalignment and velocity inductions, among others that render the precise determination of the AoA difficult (Shen et al, 2009). The AoA is indirectly obtained through pressure or velocity fields; several uncertainties are added in its estimation. In this way, determining the local AoA on wind turbine blades remains one of the greatest aerodynamic challenges. The AoA can be calculated according to its geometrical definition using the velocity triangle defined by the wind velocity and the rotational speed. This estimation relies on well-known free-stream conditions and does not take into account induction effects. If a more reliable estimation is required, it is necessary to use on-blade measurement tools
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