Parasitic effects of load introduction points in full-scale composite tidal turbine blade tests

There has been a significant increase in the development of tidal energy to enhance its competitiveness compared to other renewable sources. This growth requires dedicated fatigue testing facilities for composite tidal turbine blades. In the first decades of the tidal industry, blade load introduction methods from the wind energy sector were adopted for onshore testing. However, the relevant wind energy standards determine an unsuitable area up to one blade chord length on both sides of the blade load introduction zone from stress data analysis. This study focuses on investigating the impact of concentrated forces applied to the surface of a composite blade, particularly examining its behaviour in the inter-saddle zones. To study this effect, a full-scale composite tidal blade was tested at FastBlade using actuators. During the test, multiple measuring devices and Digital Image Correlation were employed to analyse the structural response of the blade while one of the three saddles was clamped. The clamping pressure was mapped on the blade's surface, revealing a smaller disturbed area that could reduce the number of tests required to analyse the entire blade. This disturbed area is found to vary not only as a function of the chord length, but also the blade geometry and the saddle system parameters.