Flow angle measurement of a yawed turbine and comparison to models

Abstract. The torque generated by a wind turbine blade is dependent on several parameters, one of which is the angle of attack. Several models for predicting the angle of attack in yawed conditions have been proposed in the literature, but there is a lack of experimental data to use for direct validation.

To address this problem, experiments were conducted under controlled conditions at the University of Waterloo Wind Generation Research Facility using a 3.4 m diameter test turbine. A five-hole pressure probe was installed in a modular 3D printed blade and was used to measure the angle of attack, α, as a function of several parameters. Local flow angle measurements for all azimuthal angles were obtained at radial positions of r / R = 0.55 and 0.72 at tip speed ratios (λ) of 5.0, 3.6, and 3.1. The yaw offset of the turbine was varied from −15° to +15°. Span-wise flow angle measurements are presented for the r / R = 0.55 cases, and show the variation in radial flow direction throughout yawed rotation.

Experimental results were compared directly to angle of attack values calculated using a model proposed by Morote in 2015. Modeled values were found to be in close agreement with the experimental results. The angle of attack was shown to vary cyclically in the yawed case while remaining mostly constant when aligned with the flow, as expected.

These five-hole probe measurements were also used to characterise the upstream flow profile. Wind speeds determined using the five-hole probe measurements are presented and are in agreement with measurements obtained in the wind facility during testing. The quality of results indicates the potential of the developed instrument for wind turbine measurements.