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The dynamic stall phenomenon and its importance for load calculations and aeroelastic simulations is well known. Different models exist to model the effect of dynamic stall; however, a systematic comparison is still lacking. To investigate if one is performing better than another, three models are used to simulate the Ohio State University measurements and a set of data from the National Aeronautics and Space Administration Ames experimental study of dynamic stall and compare results. These measurements were at conditions and for aerofoils that are typical for wind turbines, and the results are publicly available. The three selected dynamic stall models are the ONERA model, the Beddoes–Leishman model and the Snel model. The simulations show that there are still significant differences between measurements and models and that none of the models is significantly better in all cases than the other models. Especially in the deep stall regime, the accuracy of each of the dynamic stall models is limited. Copyright © 2012 John Wiley & Sons, Ltd.

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PROcedures for TESTing (PROTEST) and measuring wind energy systems) was a pre-normative project that ran from 2008 to 2010 in order to improve the reliability of mechanical components of wind turbines. Initiating the project, it was concluded that the procedures concerning these components should be further improved. Within the PROTEST project, complementary procedures have been developed to improve the specification of the design loads at the interfaces where the mechanical components (pitch and yaw system, as well as the drive train) are attached to the wind turbine. This is required, since in optimizing wind turbine operation and improving reliability, focus should be given to the design, not only to safety related components but also to the rest of the components affecting the overall behaviour of the wind turbine as a system. The project has resulted in a proposal for new design load cases, specifically for the drive train, a description of the loads to be defined at the interfaces of each mechanical system, as well as a method to set up and use the prototype measurements to validate or improve the load calculations concerning the mechanical components. Following this method would improve the reliability of wind turbines, although more experience is needed to efficiently use the method. Examples are given for the analysis of the drive train, pitch system and yaw system. Wind turbines still show failure rates of between 2 to 5 failures per year that need visits from technicians (derived from i.e. 1-3 ). Although electrical components and control systems fail more often, the costs related to repair of failed mechanical systems (drive train, pitch and yaw systems) are dominating the operation and maintenance costs and the downtime. For this reason, ways to improve the reliability of the three aforementioned systems need to be addressed. In depth studies, e.g., 4 and discussions with turbine manufacturers, component suppliers, and certification bodies during the Dutch Wind Workshops in Petten, the Netherlands in 2006, revealed that one of the major causes of failures of mechanical systems was insufficient knowledge of the loads acting on these components. This lack is a result of the shortcomings in load simulation models and in load measurement procedures at the level of these components.It was also concluded that, at present, the procedures, tools and guidelines in designing rotor blades and towers of wind turbines are much more specific than the procedures in designing other mechanical components such as drive trains, pitch and yaw systems. The lack of clear wind energy specific procedures in designing mechanical components and specifying the loads on these components should be resolved, thereby, preventing early failures. These wind turbine components are complex electromechanical systems themselves. Although they are indispensable in the operation of the wind turbine, these systems are, in the process of wind turbine design, usually treated as off-the-shelf systems and are purchased as such from second comp...

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