Effect on Torque and Thrust of the Pointed Tip Shape of a Wind Turbine Blade

This paper presents the effect of the tip shape of a wind turbine blade on aerodynamic forces, including the effects of separation, transition and stall. A National Renewable Energy Laboratory (NREL) Phase-VI wind turbine blade was used, in which the shape of the tip was modified to a pointed tip. Computational fluid dynamics (CFD) simulations were employed for the analysis and the results were compared with the original NREL blade CFD and experimental data using ANSYS CFX (Ansys Inc., Delaware, PA, USA). To predict the separation and separation-induced transition on both near wall and far away, the shear-stress-transport (SST) Gamma-Theta turbulent model was used. The stall onset of a 20 degree angle of attack and its effects were also analyzed and presented. The value of torque with the pointed tip blade was found to be 3%-8% higher than the original NREL blade showing the benefit of the pointed tip. Normal force coefficient is lower at the tip for the pointed tip blade, which results in lower deformation of the blade. It was found that the pointed-tip blade is more efficient in terms of generating torque than the original NREL Phase-VI blade in the dynamic stall region of 10-15 m/s wind speeds.