THE VARIATION IN WAKE STRUCTURE OF A TIDAL STREAM TURBINE WITH FLOW VELOCITY MARINE 2011

A combined Blade Element Momentum - Computational Fluid Dynamics (BEM-CFD) model is applied to a 10 m diameter tidal stream turbine blade and the supporting nacelle and tower structure in a 700 m long rectangular channel. The modelling approach is computationally efficient and is suitable for capturing the time-averaged influence of the turbine on the flow. A range of simulations are conducted for the purpose of undertaking a comparative study of the influence of the turbine on mean flow characteristics. Variations in flow structure around the turbine for different flow conditions were evaluated. Simulations are conducted for a range free-stream velocities typical of potential tidal stream deployment sites, typically up to 3.0 m s(-1). Velocity deficit profiles and wake dimensions are evaluated for each flow condition implemented. Downstream flow recovery is strongly linked to the flow velocity, and occurs over a longer distance with increasing velocity. For the range of velocities considered, some properties, such as wake length and the maximum wake length location increase linearly, or nearly-linearly with velocity. Other properties, such as the maximum wake width, and the recovery distance downstream demonstrate a tendency to converge towards a constant value. The key findings of this study highlight the significance of the free-stream velocity as an influence on the flow structure around and downstream of a tidal stream turbine.