Wind turbines are classically designed for an extremely long lifetime in machinery design terms, for example, the Siemens SWT-6.0-154 was recently certified for 25 years [1]. The implication is that wind turbines accumulate damage via a number of mechanisms. A primary concern is naturally fatigue, exacerbated by a long life (high number of cycles); however, environmental effects such as bio-fouling and leading edge erosion damage the structure but also modify the Lift and Drag characteristics, particularly the stall behaviour. Vortex Generators (VGs), more commonly known from the aviation industry, have been demonstrated to delay stall and improve the stall region characteristics. This restoration of properties has been associated with reduced fatigue loading following the logic that the rotor blade will undergo stall less severely and less often. This hypothesis was tested in this study using a newly developed fatigue tool ALBdeS (named after W. Albert the first author to write a paper considering fatigue) to post-process aeroelastic simulations conducted in FAST (from NREL/NWTC) [2]. The post processing tool is an extension of the PMV custom section rotorblade analysis tool of SMART BLADE GmbH. The ALBdeS tool calculates the cumulative damage value in each individual layer of the blade section laminates and determines whether or not failure will occur over the course of 20 years, following the GL Guidelines [3]. Sensitivity studies showed that by de-constructing the main oscillation into 30 analysis points, the accumulated damage converges to a stable result, thus increasing confidence in the stability of the method. The FAST simulations were conducted with modified versions of the NREL 5MW reference turbine. The inboard lift and drag polars of the 5MW were modified in order to simulate the effect of adding VGs to the design. The polar modifications were made in the absence of 3D stall delay effects although literature does indicate the effects are somewhat additive. However, the resulting simulations did demonstrate that VGs did in fact change the fatigue characteristics of the rotor blades but by an inconsiderate amount.

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