A laboratory study on the effects of waves on the performance and structural deflection of a tidal stream turbine

An experimental study was carried out to determine the effect of waves on a horizontal axis tidal turbine, from both power-generation and structural perspectives. Hindcast and recorded wave and tidal flow data for two locations (one in the Messina Strait in the Mediterranean Sea, the other in the Sound of Islay in the North Atlantic) was used to establish scale sample flow, under which a 1:81 scale turbine was tested in the LABIMA wave-current flume at the University of Florence. A 1:81 scale turbine model based on commercial turbine geometry was instrumented to record power output and forces acting on the support structure. Flow cases included waves of varying height and period, and flow cases ranging from benign to extreme. Waves arriving from both upstream and downstream were studied. We found that when simulating a real case of 1.3m/s flow velocity, the presence of large and long period waves (5.7m with 10.8s period) actually improved the total turbine power generation over a 25-second period. This was not the case in faster flow rate cases, when waves were detrimental to overall turbine power output. We also found that the presence of waves dramatically increase the forces applied to the turbine support structure.