Research paper: Turbine fatigue load prediction from field measurements of waves and turbulence




Authors: Hannah Mullings, Samuel Draycott and Tim Stallard

Abstract—Tidal stream turbines are placed in locations with high flow speeds in order to extract kinetic energy. These flow speeds combined with other environmental factors can lead to complex operating conditions. When
assessing turbine loading at alternative locations within a site, most models focus on velocity, shear and turbulence of naturally occurring conditions, with limited analysis including the impact of waves coexisting with currents. Previous studies have analysed the influence of wave conditions from measurements on the loading, through a consideration of the turbine not considered to be operating during large wave conditions. Although tidal conditions are often bi-directional, wave conditions are wind driven, occurring over a range of directions relative to the current; this combination will be investigated in this study. Loading on the turbine components is assessed through an efficient blade element momentum theory method, which is combined with a synthetic turbulence model to provide a time varying onset flow. This analysis focuses on full-scale site data, which was gathered at the Raz Blanchard, a potential tidal site for multiple deployments, which provides both wave and current conditions over a period of 45 days. The interest in this work is understanding the conditions which
contribute to the cyclic loading experienced by a tidal turbine. This work determines the impact of the measured waves, and the way in which they are analysed on the turbulence characteristics in the onset flow, specifically the
interaction of waves with current and influence on the loading experienced on the turbine.