Comparative study of numerical modelling techniques to estimate tidal turbine blade loads

This paper presents a method to obtain the pressure distribution across the surface of a tidal turbine blade, but without the extensive computational time that is required by 3D CFD modelling. The approach uses a combination of blade element momentum theory (BEMT) and 2D CFD modelling, where the inflow velocity vector for each blade element computed from the BEMT model is input to a 2D CFD model of each of the blade sections. To assess the validity of this approach, a comparison is made with both a BEMT and a 3D CFD model for three different blade profiles at full scale (NACA 63-8xx, NREL S814 and Wortmann FX 63-137). A comparison is also made of the NREL blade at smaller scale to investigate any Reynolds number effects on the model performance. The agreement is shown to be very reasonable between the three methods, although the forces are consistently slightly over-predicted by the BEMT method compared to the 2D-CFD-BEMT model, and the 2D-CFD-BEMT model over-predicts the pressure along the leading edge compared to the 3D CFD results. The proposed method is shown to be particularly useful when conducting initial blade structural analysis under dynamic loading.