Effects of blade tip shapes on the power output characteristics of a V-type Darrieus wind turbine

V-type Darrieus wind turbines are considered promising for floating offshore wind applications because heavy components such as generators can be located near the bottom, lowering the center of gravity, while aerodynamic loads are distributed along the rotational axis, potentially reducing overturning moments on floating structures. However, research on V-type Darrieus turbines remains limited, and effective methods for improving their aerodynamic performance have not been sufficiently clarified. Since tip losses caused by vortex shedding are a major source of performance degradation in Darrieus turbines, modification of blade tip geometry may improve power output. In this study, wind tunnel experiments were conducted to investigate the effects of end plates attached to the blade tips and winglets on the power output characteristics of a V-type Darrieus wind turbine. In addition, CFD analysis was performed for the 30° winglet configuration, which showed the greatest performance improvement, in order to clarify the aerodynamic mechanism. Experimental results showed that the end plates decreased both the maximum power coefficient and the optimal tip-speed ratio, whereas the winglets improved turbine performance. Among the tested winglets, the 30° winglet exhibited the largest enhancement in power output. CFD results revealed that the 30° winglet suppresses flow passing over the blade tip near the upwind azimuthal position, thereby maintaining strong negative pressure near the blade leading edge and increasing torque generation on both the winglet itself and the upper blade region. These findings indicate that an appropriate winglet design can effectively improve the aerodynamic performance of V-type Darrieus wind turbines.