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Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw

Author

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  • Moutaz Elgammi

    (Department of Mechanical Engineering, University of Malta, Msida MSD 2080, Malta)

  • Tonio Sant

    (Department of Mechanical Engineering, University of Malta, Msida MSD 2080, Malta)

Abstract

Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through the integration of stochastic models to be able to account for the cycle-to-cycle variability in the unsteady wind turbine blade loads under yawed conditions.

Suggested Citation

  • Moutaz Elgammi & Tonio Sant, 2016. "Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw," Energies, MDPI, vol. 9(6), pages 1-27, June.
    • Handle: RePEc:gam:jeners:v:9:y:2016:i:6:p:460-:d:72108
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    References listed on IDEAS

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    1. Sebastian, T. & Lackner, M.A., 2012. "Development of a free vortex wake method code for offshore floating wind turbines," Renewable Energy, Elsevier, vol. 46(C), pages 269-275.
    2. Farrugia, R. & Sant, T. & Micallef, D., 2014. "Investigating the aerodynamic performance of a model offshore floating wind turbine," Renewable Energy, Elsevier, vol. 70(C), pages 24-30.
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    Cited by:

    1. Elgammi, Moutaz & Sant, Tonio & Alshaikh, Moftah, 2020. "Predicting the stochastic aerodynamic loads on blades of two yawed downwind hawts in uncontrolled conditions using a bem algorithm," Renewable Energy, Elsevier, vol. 146(C), pages 371-383.
    2. Chengyong Zhu & Tongguang Wang & Wei Zhong, 2019. "Combined Effect of Rotational Augmentation and Dynamic Stall on a Horizontal Axis Wind Turbine," Energies, MDPI, vol. 12(8), pages 1-20, April.
    3. Wei Zhong & Wen Zhong Shen & Tong Guang Wang & Wei Jun Zhu, 2019. "A New Method of Determination of the Angle of Attack on Rotating Wind Turbine Blades," Energies, MDPI, vol. 12(20), pages 1-19, October.

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