Determination of the angle of attack on a research wind turbine rotor blade using surface pressure measurements

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.

Rotational and blockage effects on a wind turbine model based on local blade forces

“…These differences are up to 9% and −12% for normal and tangential force coefficients, respectively. These variations change along with the azimuthal angle and are deemed due to the differences in the inflow, where BeRT test rig presents some heterogeneity compared to the CFD simulation [19,27]. Despite the small difference, CFD results are qualitatively closer to experiments, while LLFVW has an unexpected increase between azimuthal angles 90 • − 180 • .…”

“…The experimental approaches, BeRT and the 2D-wing, use the information of pressure sensors connected through to the pressure taps located chordwise in the blade or wing, respectively. The pressure values are normalized by the relative dynamic pressure of the wind tunnel [27], which provides the pressure coefficient distribution. Datasets are (1) averaged over time at each AoA, in the case of the 2D-wing; and (2) phase-averaged at each azimuthal station over the complete set of rotations, in the case of BeRT measurements.…”

“…Since there were no pressure taps connected to sensors beyond 90% of BeRT-blade chord, the pressure integration of each dataset was performed until that chord position, in order to quantify the same contributions. Additionally, the blade pitch angle of BeRT was used to correlate it to the local AoA [27,30], based on previous work in the same test rig, Eq. 2.…”

“…A total of 31 pressure taps are located chordwise at 45% of the blade span, 12 taps on the pressure side and 19 taps on the suction side. More details on the sensors and test rig can be found in the previous work of Soto-Valle et al [27]. The acquisition frequency is set to 10kHz.…”

“…It is also perceived some sharp locations in the experiments from BeRT. These are caused by the local normalization, which changes depending on the pressure taps that provides the maximum pressure magnitude in the pressure side of the blade [27]. Figure 7 shows the normal and tangential force coefficients over azimuthal angle under a yaw misalignment of −30 • .…”