Optimization of Tow-Steered Composite Wind Turbine Blades for Static Aeroelastic Performance

The concept of passive aeroelastic tailoring is explored to maximize the performance of the NREL 5-MW wind turbine blade in a uniform flow. Variable-angle tow composite materials model the spanwise-variable wind turbine blade design to allow material-adaptive bend-twist coupling under static aerodynamic loading. A constrained optimization algorithm determines the composite fiber angles along the blade span for four inflow conditions ranging from cut-in to rated wind speeds. The computational fluid dynamics solver CRUNCH CFD and commercial finite element analysis solver Abaqus compute the static aerodynamic loads and structural deformations of the blades, respectively, which are passed iteratively between the solvers until static aeroelastic convergence is achieved. A parallel grid deformation code based on the stiffness method is developed to deform the fluid mesh based on the structural deformation of the blade. The elemental stiffness is set to the inverse of the element volume to preserve the grid quality during grid deformation.Turbine power extraction is predicted to increase by up to 14% when the blade is optimized near the cut-in wind speed, and by 7% when optimized at rated wind speed. Using the results from optimizations at discrete wind speeds, two blade design strategies are evaluated to determine a single composite layup for the blade that maximizes performance over the range of wind speeds. The first strategy uses the composite layup optimized at the rated wind speed increasing power extraction by 10% near cut-in and 7% at rated conditions, relative to the baseline blade design. The second strategy seeks a new composite layup that most closely matches the optimal blade twist at each wind speed, which results in an increase in power extraction of 14% near cut-in and 3% at rated conditions.