Due to their recent introduction there are very few data available on the mechanical response of full scale tidal turbine blades. This lack of knowledge leads to uncertainty in design and was addressed in WP4.4. Better understanding of the blade response and its limits should contribute to improved turbine reliability. IFREMER worked with Sabella to design a specific test facility and then collaborated with EnerOcean and Bureau Veritas in developing specific instrumentation.
Most tidal turbine blades are manufactured from fibre reinforced composites. They are several meters long (5 meters in the case studied here) and their break loads can be very high (10s of tons). Numerical modelling was performed in order to design a test frame capable of applying such loads in a representative way (with several load points to simulate the calculated blade loading profile).
Once the test frame had been designed and assembled the blade was mounted and instrumented. Conventional measurements were made using strain gages and displacement transducers, but more novel instrumentation was also added: Optical fibres implanted during blade manufacture provided multiple strain measurements along the blade and acoustic emission transducers provided information on damage initiation. Specific structural health monitoring transducers were also developed within the project by EnerOcean. These use an ultrasonic wave propagation network to assess the state of the blade and could be employed in service to optimize maintenance schedules.
Tests were performed in December 2020 and January 2021. The blade was loaded progressively up to first damage detection, some cycles were applied, then the blade was loaded to failure.
The test provided a wealth of information on the response of a full scale composite tidal turbine blade structure to loads representative of in-service conditions. Data are being analyzed and post-failure inspections and testing are underway, allowing recommendations to be defined to improve future blade performance.
