Seasonality of turbulence characteristics and wave-current interaction in two prospective tidal energy sites

Abstract

Velocity fluctuations caused by unsteady flows substantially increase mechanical loads on tidal turbine blades and represent a major challenge to tidal energy converters. Overcoming the challenges posed by high levels of turbulence and large waves is a significant concern for turbine developers. Here we quantify turbulence and characterize wave-turbulence interaction in two prospective tidal energy sites in Australia: Banks Strait and Clarence Strait. Turbulence characterization was derived from deployments lasting up to 3 months. Our datasets represent the longest turbulence measurements at tidal sites published to date, setting a benchmark in tidal energy site characterization. Banks Strait data was affected by wave orbital velocities at mid-water column for nearly the entire period, whilst Clarence Strait data rarely presented significant wave-turbulence interactions. Turbulence intensities varied mostly between 12% and 17% in both sites. Higher turbulent kinetic energy density was observed in Banks Strait, although one of Clarence Strait stations revealed faster current speeds exceeding 2.8 m/s. Investigation of strong wind events suggests turbulence parameters were not majorly affected. Our findings are valuable to obtain more realistic turbine performance and loadings estimates from numerical models and considerably contribute towards efforts to establish best-practice turbulence assessment methods in tidal energy sites.