Nonlinear flutter analysis of a bend-twist coupled composite wind turbine blade in time domain

Abstract

Modern wind turbine blade having large slender structure are vulnerable to aeroelastic instability. Aeroelastic tailoring through bend-twist stiffness coupling is an effective way to improve the aeroelastic performance of such large blades. Effect of geometric nonlinearity is significant in these blades. This study presents a time domain aeroelastic analysis followed by a detailed parametric study of large composite wind turbine blade considering von-Karman nonlinearity in the strain–displacement relationship. Flutter limits of three MW sized namely, NREL 5 MW, SNL 61.5 and SNL 100–00 wind turbine blades considering and without considering geometric nonlinearity are compared. A parametric study of SNL 61.5 is conducted by changing the lamination sequence in the spar cap and all section of blade considering the symmetric and asymmetric skins. It has been observed that both nonlinear and linear structural models i.e., models considering and without considering geometric nonlinearity predict highest flutter speed at the same blade configuration and lamination sequence. However, there is a significant difference in the flutter speeds predicted by these models.