The larger stress and strain concentration will be caused in some positions of the blade by the coupling action of gravity, centrifugal force and aerodynamic load in the rotation process, which can reduce the reliability and life of wind turbine. Most of the blades with hollow thin-walled structure are made of glass fiber reinforced composite material, and the optimal design of internal structure and fiber layer is used to improve the strength and rigidity. Furthermore, the aerodynamic force that is the main power source changes with the wind speed all the time. Therefore, it is of great theoretical significance of guidance and engineering value of application to perform the accurate and real-time extraction of aerodynamic force, and optimize structural geometry parameters and composite layer for the blade under the coupling effects of multiple loads. The optimization can ensure safe and stable operation of wind turbine. However, the investigation about the structural optimization of vertical axis wind turbine (VAWT) blade considering the time-varying load effect is few. In the present study, the multi-objective structural optimization design of the blade was performed to improve the structural performance of H-type VAWT when the multi-loads were coupled. First, the transverse stress, longitudinal stress, shear stress and strength ratio under the bending deformation of beam whose constraints and forces were similar to those of the blade, were obtained by analytical and finite element methods. The results of two methods were compared to verify the correctness of finite element analysis process. Moreover, the trailing-edge of NACA0021 airfoil was modified with the coordinate rotation and coefficient zoom, and then the airfoil's middle arc line located on the circumference of wind wheel. The sharp tailing-edge airfoil with certain camber, namely NACA0021SC, was obtained. Furthermore, the parametric finite element model of the blade with new airfoil was established with the APDL language. The pressure distribution on the blade surface was calculated by FLUENT, and the aerodynamic force extracted accurately and in real-time by the FSI mapping method was applied on mesh elements of the blade structure to realize the aerodynamic force transfer between FLUENT and ANSYS. Finally, the particle swarm optimization (PSO) algorithm, which was improved through the cosine adaptive of inertia weight and dynamic adjustment of learning factor, was applied for the structural optimization by taking the minimum blade mass and maximum laminate strength ratio as design objectives. The results showed that the mass of single blade at different azimuth angles of 90°, 180°, 270° and 360° decreased by 13.70%, 11.85%, 8.09% and 9.60% after optimization, respectively. The maximum stress and strain decreased by as much as 20.71% and 23.77% at the azimuth angles of 90° and 180°, the biggest decline of maximum displacement was 9.34% at the azimuth angle of 360°, and the reciprocal of strength ratio reduced mostly at the azimuth angle of 180° by 9.38%. To the wind turbine, the mass, maximum stress, maximum strain, maximum displacement, and maximum reciprocal of strength ratio decreased by 7.51%, 8.50%, 20.20%, 1.90% and 16.11%, respectively. The stress concentration and deformation decreased and the strength increased, which indicated that the structural performance was enhanced. The research can provide significant guidance for structural optimization of wind turbine blade with time-varying load. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
