Effects of wave-current interactions on the performance of tidal stream turbines

Ordonez Sanchez, Stephanie and Porter, Kate and Frost, Carwyn and Allmark, Matthew and Johnstone, Cameron and O'Doherty, Tim (2016) Effects of wave-current interactions on the performance of tidal stream turbines. In: 3rd Asian Wave and Tidal Energy Conference, 2016-10-24 - 2016-10-28, Marina Bay Sands.

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The main objective of this paper is to analyse extreme cases of wave-current interactions on tidal stream energy converters. Experiments were undertaken in the INSEAN tow tank facility where carriage speeds of 0.5 and 1m/s were used with and without waves. The waves studied in this testing campaign had wave heights of 0.2 to 0.4m with a 2s wave period in a stationary reference frame. These wave conditions were considered extreme cases considering the use of a turbine with a rotor diameter of 0.5m. The turbine was equipped with a torque transducer, an encoder and a strain gauge to measure both the rotor torque and the forces on a single blade root. The results of the experiments showed that extreme wave-current cases can result in significant variations in power. Investigating the time histories of the blade root loading in wave-current conditions illuminated the importance of the relationships between the wave phase and blade angular position, and the number of blade rotational periods in a wave period. These affected the loading patterns and also the loading range seen by the blade, both of which have important implications for the fatigue life of the blade.