Structural performance of composite tidal turbine blades

Abstract

Tidal turbine blades experience a significant bending moment in the root area during their long-term operation in a sea water environment. This necessitates using fibre reinforced polymer as the blade material to provide the required strength/stiffness. In this study, a design methodology based on hydrodynamic and Finite Element models with a view to examine the mechanical properties of composites was developed to evaluate the structural response of two commercial scale turbine blades (1.5 and 0.35 MW). Using the output from the hydrodynamic model, Finite Element stress analysis was conducted in order to determine the likelihood of blade failure. To incorporate appropriate failure modes with the blade model, failure analysis was conducted on the composite test coupons. The results of stress analysis show that the blade root area experiences high stress values with failure modes such as resin cracking, fibre/matrix interfacial de-bonding, delamination and fibre breakage. It is also predicted that the glass fibre composite blades require three times thicker laminates than a carbon fibre composite blade of similar design to maintain the same safety factor. Reasonable agreement between the numerically and experimentally determined strain fields on a small-scale blade indicates that the result of Finite Element stress analysis is valid.