A Preliminary Comparison of 2D and 3D Open Models for Tidal Stream Energy Applications

The tidal energy sector is transitioning from deploying single tidal turbines to large-scale arrays. Efficient and high-performance numerical modelling is crucial for determining the array layouts and accurately predicting the annual energy yield of tidal farms. For this, 2D and 3D regional-scale hydrodynamic models have been developed to assess wide-area tidal resources and model turbines over large areas and extended time periods. Although 2D models are more computationally efficient than 3D models for predicting regional flow, the differences in flow prediction performance between 2D and 3D regional-scale models requires further study for tidal energy applications. This study compares 2D and 3D flow predictions at the European Marine Energy Centre (EMEC) tidal energy test site in Scotland using the open software Telemac2D and Telemac3D. Both models are validated against Acoustic Doppler Current Profiler (ADCP) measurements obtained from a legacy UK tidal project (ReDAPT, 2010–2015). Our analysis evaluates the differences in depth-averaged velocities and energy yield predictions between the 2D and 3D model at two locations which are approximately 80 m apart but with large variation in flow regime observed in our previous studies. The evaluation is conducted on three different turbine scenarios with turbines occupying different regions in the water column. Our approach to 2D model evaluation uses a simplified power law assumption to convert depth-averaged velocities into velocity profiles and showed significant deviations in predicted energy yield compared to the 3D approach, which directly calculates power-weighted rotor averaged velocity taken from the velocity profiles. Model prediction differences are shown to be greater for turbine rotors located higher in the water column. The findings motivate further studies on modelling tool selection for tidal energy applications, taking into account machine type and levels of spatiotemporal variation at the side under study.