Effect of icing on the aerodynamic performance of commonly used airfoils in wind turbine blade tips

Icing has posed the significant impact on the aerodynamic performance and power output in wind turbines, particularly on the airfoil at the blade tip position. Therefore, it is particularly important to evaluate the performance of wind turbines before and after icing for real operating. According to the conditions of GW87/1500 wind turbine, this study aims to analyze the icing behavior of the blade tip airfoils and the aerodynamic performance using computational fluid dynamics. The objects were also adopted as the commonly-used DU-96W-180, DU-95W-180, and S810 airfoils at the blade tips of the wind turbine. Three kinds of operating conditions were set as the light, medium and heavy icing. The results show that there were the similar icing mass, thickness and limit of DU95-W-180 and DU96-W-180 airfoils. The smaller icing mass and thickness were found on the S810 airfoils; Under the light icing conditions, the angles of attack corresponding to the maximum lift-to-drag ratios of the three airfoils were the same as those under the un-iced condition, which were about 7°. The angles of attack were advanced from 13° to about 11°, corresponding to the peak lift coefficients of the DU96-W-180 and DU95-W-180 airfoils. While the aerodynamic performance of the S810 airfoil was deteriorated more significantly, where the angle of attack was advanced from 13° to about 9° corresponding to the peak lift coefficient; Under the moderate icing conditions, the angles of attack were still about 7° corresponding to the maximum lift-to-drag ratios of DU95-W-180 and DU96-W-180 airfoils, while those of S810 airfoils were advanced to around 5°. The peak lift coefficients were advanced from 13° to 9° corresponding to the peak lift coefficients of the DU96-W-180 and DU95-W-180 airfoils, while those of the S810 airfoils were advanced from 13° to 5°. Moreover, the lift and drag coefficients varied even more drastically. The aerodynamic performance of the three airfoils decreased more significantly under heavy icing conditions. The pressure distribution and surface flow pattern of the blade tip airfoils were measured under different icing conditions. There was the destroyed distribution of surface pressure on the three icing airfoils. The pressure coefficient at the leading edge of the airfoils was oscillated to reduce the lift, indicating the decreasing difference of pressure. There was the great variation in the flow distribution on the airfoil surface before and after icing of the three blade tip airfoils at 5° angle of attack. There was the increase in the separation vortices between the leading and trailing edge position of the DU95-W-180, DU96-W-180, and S810, when the icing condition was ranged from the light to the heavy. The flow separation was aggravated at the boundary layer of the airfoil surface. The better aerodynamic performance of DU96-W-180 airfoil was achieved before and after icing. The finding can be applied to optimize the airfoils of wind turbine blades in cold regions, in order to improve the energy utilization efficiency of wind turbines.