Research on Drag Reduction Characteristics of Wind Turbine Airfoil Surface Microstructure

Abstract

The objective of this work is to investigate the effect of the bionic microstructure surface on DU21 aerofoil. The motivation behind this study is to investigate the effect of the bionic microstructure parameters including the location, interval between two microstructures, groove sizes of microstructure under different working conditions in order to improve the drag reduction characters. The numerical simulation is performed on the bionic microstructure model using the RNG k-ε model. It is found that: when the groove size is less than 0.15 mm, the drag can be reduced with any inflow speeds. When the groove size is 0.2 mm or 0.3 mm, the drag reduction effect can be achieved only when the inflow speed is relatively small. The resistance increases with any inflow speed when the groove size is up to 0.5 mm. The viscous resistance gradually increases, and the differential pressure resistance gradually decreases with the interval size increasing. There is a minimum resistance value when the groove depth h = 0.075 mm and the maximum drag reduction rate is up to 3.62%. Drag reduction mechanism of the microstructure was also studied. When the fluid passes through the microstructure, a stable reverse vortex flow is formed inside the groove, so that there is no direct contact between the fluid and the wall surface, thereby achieving a drag reduction effect. The vorticity values inside the grooves of the microstructure are smaller than that of the smooth airfoil and the turbulent kinetic energy and turbulent dissipation rate at the bottom of the groove are very small.