The development and validation of a new joint system for sectional blades is presented in this paper. The system is a bolted connection located in the blade spar cap, and its geometry accommodates a higher number of bolts than any other conventional solution requiring inserts. This results in higher transmitted loads per spar cap width.The modular concept of the system is composed of cell units that can be easily integrated into the design and manufacturing of different blade architectures and used in blades of various lengths by selecting the appropriate number of cell units.The design of the system was performed using analytical and finite element analyses. The analyses were validated using risk reduction mechanical tests, which resulted in an optimized joint system. The loads to be transmitted by the joint system were calculated according to IEC61400-1 using the GH-Bladed Version 3.80 on a 5 MW onshore class II-A wind turbine with a tower height of 120 m and a 61.5 m blade with double spar webs. The joint system was successfully tested in a fullscale mechanical test for its validation under Germanischer Lloyd guidelines and supervision.
Some wind turbines have exceeded their nominal design service life and are continuing their operation with periodic inspections and maintenance. In the case of rotor blades, the reliability of the inspection is very limited because of the blade structure that comprises laminates and sandwich structures, which are very difficult to monitor. For this reason, wind farm owners are searching for technologies or approaches that will guarantee a safe operation of their wind turbines after the design life has elapsed. The main objective of this paper was to investigate whether detection of ageing of wind turbine blades using deflection as key parameter is feasible using commercial equipment. The paper is divided in three phases. In phase 1, the effect of ageing on a new UD‐0° glass fibre with high moduli was obtained. Using these results and bibliography data, a theoretical study was performed in phase 2 to determine the magnitude of blade deflection along its lifetime due to material ageing. Finally, in phase 3, in‐field deflection measurements where performed on a wind turbine blade to evaluate the utility and limitations of commercial equipment for the detection of blade ageing. It was concluded that material ageing could result in an increase in blade deflection under self‐weight that can be detected using commercial measurement equipment. These results can be used by wind farm owners in their O&M strategies to monitor blades over time and decide whether they should be repaired or replaced.
The impact of wind turbine (WT) blade erosion is still a major issue today because of the associated high maintenance costs and the loss of power production. The erosion process is influenced by many physical phenomena that still need to be understood better. Especially WT manufactures and owners need to know the potential impact of different levels of blade erosion on annual energy production (AEP). The damage produced by erosion modifies the aerofoil shape and therefore its aerodynamic properties, resulting in an AEP drop. In this study, the effect of various morphologies of erosion on AEP was obtained. First, a 3D characterisation of eroded blades using a laser scanner was performed. The erosion damages were grouped into two typologies: Typology 1 covers pits and gouges, and Typology 2 covers extended loss of top coat. Based on this, 2D section geometries were defined to evaluate the effect of erosion on the aerofoil aerodynamic 2D properties, which was done using the CFD code WMB. The aerofoil used as a reference was DU96W180. It was determined that the erosion damage alters the aerodynamic behaviour of the aerofoil by reducing the Cl max and the slope of the Cl- α curve, which resulted in a drop of the aerodynamic efficiency from 40% to 72%. These detrimental effects increased depending on the damage location (i.e., pressure side and closeness to the leading edge), damage size and shape (i.e., sharp transitions from the eroded to non-eroded surfaces). To evaluate the erosion effect on the AEP, the NREL 5 MW WT was selected. All its components were kept except the last 30% outer section of the 61.5 m blade whose NACA64_A17 aerofoil was replaced by a DU96W180. The erosion damages were modelled by extending the 2D eroded geometry along this outer section. The AEP was calculated using BLADED 4.5. It was concluded that erosion resulted in a decrease of the AEP, which can be up to 1% and 6% for damages of Typology 1 and 2, respectively. This study will help to standardize and estimate the effect of the type of erosion on AEP losses for different shapes and erosion typologies.
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