Structural design and analysis of composite blade for horizontal-axis tidal turbine

Abstract

In this work, we report on the structural design of a 5-m-long composite blade intended for use in a horizontal-axis tidal turbine. The blade geometry is constructed through an optimization process to obtain the maximum power coefficient at the desired tip speed ratio of 4.5 by applying the blade element-momentum theory (BEMT). The blade is primarily designed using a NACA 63-424 hydrofoil. The blade structure is designed by using the BEMT to compute the loading conditions at various inflow velocities. Two parallel spars were chosen to produce the blade structure grid, and the preliminary lay-up structure of the composite blade was determined according to the thickness distribution identified using the twisted beam theory under the assumption that the two spars plus the upper and lower skins mostly contribute to the flap-wise bending stiffness while withstanding an external load. Then, high-strength unidirectional and double-bias fiber glass/epoxy materials were chosen to fabricate the blade. The final blade structure was then analyzed in ANSYS Workbench using the finite element method. The results show that the blade structure can withstand the applied load with failure indices <0.4.

Keywords

• beam theory
• composite blade
• lay-up structure
• loading condition
• spars
• structural design