Wind turbines often operate in challenging environmental conditions. In hot and dusty climates, wind turbine blades are constantly exposed to abrasive particles that, according to many field reports, cause significant damage to the blade’s leading edge. On the other hand, in cold climates similar effects can be caused by prolonged exposure to hail and rain. The trailing-edge of modern turbine airfoils is also often subject to damage according to industry veterans, which can be caused during the transportation and assembly phases and by wear and tear during operation. Quantifying the effects of airfoil deterioration on modern multi-MW wind turbines is crucial to correctly schedule maintenance and forecast the potential impact on productivity. Analyzing the impact of airfoil damage on fatigue and extreme loading is also important to improve reliability and longevity of wind turbines and is a topic that has not yet been extensively investigated.

The aim of this work is to develop a numerical modeling strategy for blade erosion and evaluate the performance deterioration and the impact on loading of this phenomenon. The DTU 10MW RWT is used as platform for this study as it is representative of the size of the future generation wind turbines. Such large machines can operate with Reynolds numbers higher than 12 million, where little airfoil polar data is available let alone eroded airfoil data. An extensive literature review of the topic is discussed. A blade erosion model is developed: the shape of the leading and trailing edge of airfoils is modified to mimic the effects of this phenomena. The lift and drag of the eroded airfoils are calculated with CFD for angles of attack ranging between -20° and 30° and extrapolated for the full 360°. Nine stages of deterioration for the FFAW3-301 and FFAW3-241 airfoils, which constitute the outer part of the blade, are calculated by combining three stages of leading-edge and three stages of trailing-edge damage.

Power and torque coefficients are compared in idealized conditions at rated wind speed, at a wind speed above rated and one below rated, showing significant differences up to more than 5%. Full aero-servo-elastic simulations of the DTU 10MW RWT are conducted with the eroded polars using NRELs BEM-based code OpenFAST. Sixty-six ten-minute simulations are performed for each stage of airfoil damage, reproducing operating conditions specified by IEC61400 high turbulence power production DLC-group, including wind shear and yaw misalignment and turbulence. Damage equivalent loads (DELs), which are a common way of comparing fatigue loading levels in the wind turbine industry, are compared and the differences are discussed. Blade-root and tower-base bending moments, tower-top and blade-tip deflections are considered, as well as control sensors like blade pitch and rotational speed. Lifetime DELs allowed the assessment of the global differences caused by erosion, while wind-bin averaged 1Hz DELs were useful to understand which conditions are causing the most differences. Extreme values of the main turbine loads are also compared. Annual Energy Production (AEP) for the turbine, simulated in IEC class I-IIIA, is also compared, with preliminary results showing as high as 6.5% decreases.


Numerical Modeling of the Effects of Leading-Edge Erosion and Trailing-Edge Damage on Wind Turbine Loads and Performance

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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