Blade shape evaluation for cross-flow tidal turbines—A fast and automated assessment tool for early design stage based on power and load coefficients

Cross-flow tidal turbines (CFTT) are a promising technology for tidal energy exploitation. They are omni-directional, feature high area-based power density and a simple design. However, due to their rotation around the vertical axis, the blades undergo a continuous change in their angle of attack, leading to alternating loads, which can cause fatigue failure. For this reason, blade loads should already be taken into account in the early design phase. This study presents a standardized and automated method for evaluating the influence of blade profile shapes on power and load coefficients. Fully automated computational fluid dynamics simulations are coupled with an analytical mechanical model, treating blades as a clamped beam. This allows for evaluation of the turbine's performance (power coefficient CP) and the structural load. A stress coefficient Cσ is introduced to quantify fatigue risk by taking both amplitude and mean stress into account. The methodology is applied to 120 randomized blade shapes with different operating points. Results indicate that a stronger blade cambering reduces CP, while Cσ remains unaffected. Nevertheless, the blade's chord length and operating point show a weak correlation with Cσ. An additional detailed analysis of four arbitrarily selected cases and the reference case is conducted. The findings highlight the importance of optimized blade geometries to balance the power output and the structural lifetime of CFTTs.