Abstract
Tidal stream energy has emerged as one of the most promising alternative energy sources to the use of fossil fuels. Nevertheless, there are some crucial issues that must be overcome. One of these key aspects is the response of tidal stream energy converters to the extreme velocities related to high-frequency velocity perturbations from the mean current speed. In this study, the dependence of this velocity fluctuation on the turbulence conditions of the flow is analysed based on the data measured during 1 week by two Acoustic Doppler velocimeters in two tidal channels in the Goto Islands, Japan. At one of the channels, where maximum 3-min averaged measured velocity is 1.7 m/s, extreme values over 3 m/s were observed. Turbulence intensity ranges between 10 and 35%, with a clear contrast between flood and ebb conditions at one of the measuring points. Peak velocity, in terms of a peak-to-averaged ratio, and turbulence intensity calculated for 3-min periods were compared, obtaining linear trends with similar slopes for both measuring points and under different flow conditions. Since turbulence conditions can be simulated by numerical modelling, the presented correlation opens the door to prediction of extreme velocities, reducing the need for in situ measurements.