Copenhagen Class – A New Concept for Wind Turbine Blade Design
Pre-design Evaluation by Risø Technical University of Denmark
The pre-design evaluation phase consists of interim sub-component tests to verify the design for which numerical tools and design criteria are sufficient. Furthermore, the design will be reviewed by Risø DTU with a view to both aerodynamic and structural feasibility in comparison with the required specifications and design criteria. This phase will go hand- in-hand with and parallel to the pre-design phase. A typical layup is not particularly well suited to reduce cap deflections, since the fibres are mainly placed in the longitudinal direction of the blade. The lack of fibres in the transverse direction causes the cap to be relatively flexible in the lateral direction. When the cap deflects there is a risk of transverse tension failure in the unidirectional laminates. Furthermore, it is common that manufacturing imperfections inside the laminate further reduce the fatigue and ultimate strength of the laminate.
Detailed Design
The detailed design phase is a summing up of all the results from the previous phases and, based on the results from the pre-design phase, applying the final adjustments according to results from the feedback of the pre-design verification phase. The technical reports and drawings with ply books and layup design are produced and sent to the certification body for approval.
Design Evaluation by Risø Technical University of Denmark
The design evaluation is a final review by Risø DTU of both aerodynamic and structural feasibility in comparison to the required
specification and design criteria. A full-scale test performed recently at Risø DTU validated the results from the numerical simulations. The 34m blade from SSP Technology, which was tested in full scale, was not part of a certification process, but of a research project designed to find out how critical current and future blades are to sustain this combined load scenario.
Tests with combined flap and edge loads have been carried out with the load application on the suction side and with an angle of attack of 30 degrees from the flap plane. A communicative report for later marketing of the Copenhagen class concept will be delivered to the customer and the blades will be supplied with the Copenhagen class logo.
Test and Verification
Test and verification is carried out according to the requirements of the certifying body, including a combined flap and edge load scenario. This will be carried out as a more realistic load case by use of the methods developed by Risø DTU, which allows the blade to move freely compared with conventional attachment systems where the blade is restricted in its movements and thus reinforced due to the test set-up. The test results will be reviewed by Risø DTU, and will be part of the communicative report delivered to the end-customer.
The Copenhagen class concept pools experience, know-how and proven technologies from two highly specialised organisations in wind energy to accommodate the need for lightweight, reliable and cost-effective large blades for the wind turbines of the future. n
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Breathers&bleeders
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