WINDFLOWER · Aeroelastic tailoring of a passive wind turbine rotor and validation of design code

Periodic Report Summary - WINDFLOWER (Aeroelastic tailoring of a passive wind turbine rotor and validation of design code)

Project context and objectives The main objectives of these first two years of the WINDFLOWER project were to chart the possibilities of a highly flexible wind turbine rotor by building a detailed model in the aeroelastic Horizontal Axis Wind turbine simulation Code 2nd generation (HAWC2) and evaluating its behaviour under different configurations. Further, the upcoming wind tunnel experiments in the Open Jet Facility (OJF) of the Delft University of Technology (TU Delft, Netherlands) are to be prepared. Secondary objectives arise in the broader context of a PhD study at the Technical University of Denmark, Risø campus (Risø-DTU). This mainly concerns following courses at a Masters and PhD level, at Risø-DTU and elsewhere, for a total of 30 European Credit Transfer and Accumulation System (ECTS). Project Activities A short description of the work performed since the beginning of the project: - Risø technical report on swept blades (publicly available); - Publication as co-author on load extrapolation method in a leading wind energy and peer reviewed journal (Wind Energy, published by Wiley). The article is in proof editing phase, but the publication date is not yet known; - Presentation at the European Academy of Wind Energy (EAWE) PhD seminar 2010 in Trondheim, Norway (static yaw stability); - Poster presentation at the European Wind Energy Association (EWEA) 2011, largest European wind energy conference (dynamic yaw stability); - Programming of framework for pre- and post-processing tools to be used with the aeroelastic wind turbine simulation program HAWC2 . Due to the large amount of simulations and results, this work is an important part of the project; - Participation as a speaker at the Marie Curie celebration (Dec 2010). This event was held to symbolically celebrate 50,000 Marie Curie fellows; - Completed courses at Risø-DTU for a total of 20 ECTS including advanced digital signal processing, laminate and sandwich structures, scientific paper writing in English, wind turbine load analysis with HAWC2; - Preparations for the wind tunnel tests in the OJF at the TU Delft have started. The OJF experiments are now scheduled for the beginning of February 2012. A brief overview of the main activities: - Interactions with TU Delft regarding planning, measuring techniques and model construction for the OJF; - Downscaling and design of the wind turbine prototype for the OJF and simulation model for HAWC2 from full-scale (appr. 24 m rotor diameter) to the OJF scale (appr. 1.8 m rotor diameter). Project results Intermediate results During the first part of the WINDFLOWER PhD project, different flexible wind turbine rotor topologies were investigated. In the conference papers published (EAWE PhD Seminar 2010 in Trondheim and EWEA 2011) it was shown that rotor flexibility helps in stabilising a free yawing wind turbine in downwind configuration. However, an unstable region remains and will be the subject of further investigation for both numerical simulations as wind tunnel experiments. Results so far suggested that the aerodynamic design of the inner part of the rotor diameter contributed to these instabilities. Since the aerodynamic data and modelling of the inner part of the rotor diameter is lacking sufficient accuracy (a well-known uncertainty in the wind energy industry which still remains unanswered), the wind tunnel tests will need to clarify and confirm these instabilities. The programming framework for pre- and post-processing tools in combination with the aeroelastic simulation tool HAWC2 is another tangible result from the work performed up to now. Although it is not trivial, the result is only a practical tool and is used on a daily basis. Expected final results The wind tunnel tests in the OJF will be used to show the validity of the aeroelastic simulation code HAWC2 for flexible rotor configurations in general. Since the downscaling from full-scale to OJF prototype scale will not preserve all required similarities, it will not show the validity of the flexible rotor concept on a one-to-one basis. However, it is expected to show which design parameters of the flexible rotor concept are beneficial for stable and safe operation.

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