Numerical analysis of blockage correction methods for tidal turbines

Abstract

The current work presents the analysis of six different blockage correction methods for axial-flow turbines from the literature and compares them to a method proposed by the authors using blade-resolved CFD simulations. The analysis of the different methods is performed by comparing the corrected blocked-flow thrust and power results of a tidal turbine to a quasi free-flow condition, obtaining a quantitative measure of the error for every method at different blockages and tip-speed ratios. This study shows that not every available method for blockage correction remains valid for the range of turbine thrusts that may occur in blocked flows. Of the seven methods analysed, only three were found to provide a reliable estimate of the power and thrust across the range of blockage and tip-speed ratios analysed in this paper, including the one proposed by the authors. Of the remaining correction methods, those that could be used as a first approximation for low-blockage conditions are identified.