Aerodynamic, structural and aero-elasticity modelling of large composite wind turbine blades

Large wind turbine blades, manufactured from fibre reinforced laminated composite materials, are key structural components of wind turbine systems. The demands for efficient and accurate modelling techniques of these composite blades have significantly increased. Over past decades, although complex computational models have been widely developed, more analytically based models are still very much desired to drive the design and optimization of these composite blades forward to be lighter, stronger, efficient and durable. The research work in this thesis aims to develop such more analytically based aerodynamic, structural and aero-elasticity models for large wind turbine blades manufactured from fibre reinforced laminated composite materials. Firstly, an improved blade element momentum (BEM) model has been developed by collectively integrating the individual corrections with the classic BEM model. Compared to other existing models, present BEM model accounts for blade tip and root losses more accurately. For laminar flow, the 3-D cross-flow is negligibly small. In this case, present BEM model with statically measured 2-D aerodynamic coefficients agrees closely to experimental measurements. However, stall delay correction is required for a 3-D rotating blade in stall. A new stall delay model is developed based on Snel s stall delay model. Verifications are performed and discussed for the extensively studied NREL UAE phase-VI test. The predictions of distributive and collective factors, e.g. normalised force coefficients, shaft torque and etc. have been compared to experimental measurements. The present BEM model and stall delay model are original and more accurate than existing models. Secondly, significant deficiency is discovered in the analytical thin-walled closed-section composite beam (TWCSCB) model proposed by Librescu and Vo, which is widely used by others for structural modelling of wind turbine blades. To correct such deficiency, an improved TWCSCB model is developed in a novel manner that is applicable to both single-cell and multi-cell closed sections made of arbitrary composite laminates. The present TWCSCB model has been validated for a variety of geometries and arbitrary laminate layups. The numerical verifications are also performed on a realistic wind turbine blade (NPS-100) for structural analysis. Consistently accurate correlations are found between present TWCSCB model and the ABAQUS finite element (FE) shell model. Finally, the static aero-elasticity model is developed by combining the developed BEM model and TWCSCB model. The interactions are accounted through an iterative process. The numerical applications are carried out on NPS-100 wind turbine. The numerical results show some significant corrections by modelling wind turbine blades with elastic coupling.