Design optimization of endplate for a small H-Darrieus vertical axis wind turbine at a low tip speed ratio

The endplate for a small H-Darrieus vertical axis wind turbine is optimized using a global optimization method with three-dimensional computational fluid dynamics (CFD) simulations. This study focuses on the design of a three-bladed wind turbine characterized by a diameter of 0.2 m, a height of 0.2 m, and an operational tip-speed ratio of 0.7. The design process is conducted in the following two phases. First, CFD simulations are performed on various endplate topologies to identify a potential one. Second, an aerodynamic shape optimization is performed on the potential topology using the framework of the surrogate model-based global optimization approach. The performance of wind turbines is evaluated using unsteady Reynolds-averaged Navier–Stokes simulations. The potential design obtained in the first phase (investigation of various topologies) is a three-pronged endplate whose outlines are defined by quadratic curves. The optimized design obtained in the second phase (shape optimization) covers more around the leading edges and less around the trailing edges of the blade airfoils than the baseline design obtained in the first phase. The optimal endplate generates low-pressure regions around the leading edge when the position of the blade is at a rotational angle of 0°. This enables a larger thrust force to be generated, thereby achieving an additional 4% improvement in performance compared with the baseline design. This performance improvement is also reproduced in wind tunnel experimental evaluations.