A Study on Various Aerodynamic Effects of Pointed Tip Blade

Abstract

A wind turbine blade performance depends on various parameters of which the shape of the blade is one of the most important one. In this work the shape of the tip of original NREL Phase-VI blade (S809 airfoil) has been modified to determine the changes in the blade aerodynamic performance. The chord length of new blade is kept similar to the original NREL blade up to 90% of the span. Last 10% was modified to a pointed tip at the pitch axis. This paper presents a comparative study of the effect of pointed tip on aerodynamic loads. CFD simulations were performed on both original NREL shape and pointed tip shape blades. The simulation results of pointed tip blade were compared with both experimental and simulation results of original blade. Ansys geometry modeler was used to draw the geometry and to generate the grids. Ansys CFX solver and post processor were used for simulation and calculation of the results. To predict the near wall transitional effect SST Gamma Theta turbulence model was used. Results of pressure coefficient along the chord at various blade sections of the pointed tip blade were found to be almost similar to the original NREL blade CFD results. Tangential and normal force along the span of pointed tip blade at different wind speeds showed some similarity in results compared with CFD results of original NREL blade. From the velocity contour the separation of flow with the increase of wind speed can clearly be observed. Thrust and torque effects are also observed at various wind speeds. The torque values for the pointed tip blade were found to be higher in the pre-stall and stall region but slightly lower in post-stall region. But compared to the torque values the difference in thrust at the same region is found to be negligible. Pointed tip thrust values are in better agreement at high wind speeds with respect to the experimental data. The flow separation at high wind speed is also found to be less with pointed tip blade compared to the original blade.