The coupled Blade Element Momentum - Computational Fluid Dynamics (BEM-CFD) model offers a computationally efficient tool for simulating Tidal Stream Turbines (TSTs). The model is used to evaluate TST performance through simulations over a range of tip speed ratios and flow velocities. When compared to other modelling approaches, such as classical Blade Element Momentum Theory (BEMT) or pure CFD modelling, the coupled model has a tendency to over-predict rotor performance. When compared to CFD results with geometry-defined blade surfaces, the model is computationally less expensive but under-predicts wake recovery. One possible reason for this is that the source terms used to represent the rotor are only introduced into the momentum equations of the CFD model, and not the turbulence equations. This paper will attempt to address this aspect by introducing an additional term to the dissipation rate equation of the standard k-? turbulence model. The purpose of this term is to represent the breakdown of large-scale turbulence to small-scale turbulence at the location of the blades. Variation in the value of this additional term with flow velocity and tip speed ratio of the rotor will be evaluated.
