LES of a Marine Current Turbine with Tidal Waves

Interest and investment in the renewable energy sector is presently increasing due to the need to reduce carbon emissions from electricity generation and to diversify national electricity generating portfolios. Systems for generating useful electricity from the natural resource of tidal streams are of particular interest in the UK. Such systems typically comprise arrays, or farms, of tidal stream turbines (TST). Over the last decade, the design of tidal stream devices has progressed rapidly and several horizontal-axis turbines are now undergoing prototype trials at offshore test sites. However, there is limited understanding of how the loading, power output and wakes of TST are affected by the ambient turbulence of the tidal flows that are suitable for energy extraction. The aim of this work is to use detailed CFD investigations via blade resolved RANS and LES to understand the flow physics and predict the behaviour of such a device under different operating conditions. A CFD model has been developed for this purpose and applied to two turbine geometries: scale experiments and a full-scale turbine developed by Tidal Generation Ltd. (TGL). Particular attention is given to the influence of turbulence characteristics and waves on loading and performance.