Numerical Investigation of Effects of Surface Roughness on Dynamic Stall Characteristics of FFA-W3-241 Wind Turbine Airfoils

During the operation of large wind turbine blades, surface roughness structures of varying scales are formed, and the dynamic stall characteristics of airfoils are significantly altered by these structures. Dynamic stall analyses have been predominantly conducted on smooth airfoils in existing studies, while systematic investigations into the effects of surface roughness on airfoil dynamic stall performance remain insufficient. In this study, the FFA-W3-241 airfoil, widely applied in large wind turbines, was selected as the research object. Numerical simulations were performed using the unsteady Reynolds-averaged Navier–Stokes approach, and the pitching oscillation of the airfoil was implemented using the overset grid technique. A smooth airfoil configuration and multiple roughness configurations were established, and unsteady aerodynamic computations were carried out under deep and light dynamic stall conditions, respectively. The effects of surface roughness on dynamic stall were analyzed from aerodynamic hysteresis, surface pressure distribution, and flow field characteristics. The results indicate that the leading-edge suction peak is significantly attenuated by surface roughness, and a more gradual pressure distribution is produced, resulting in a reduction in the maximum lift coefficient and an increase in the drag coefficient as the roughness level rises. The scale of the trailing-edge vortex is expanded, and the flow separation region is enlarged. The area of the hysteresis loop is reduced. Under deep dynamic stall conditions, the lift hysteresis curve transitions from an abrupt drop to a gradual decline. Dynamic stall load fluctuations can be mitigated by surface roughness, whereas the aerodynamic efficiency of the airfoil is permanently degraded. The findings of this study can provide a theoretical reference for wind turbine blade design and load calculation.