On lift enhancement and noise reduction in serrated gurney flap airfoil of wind turbines using proper orthogonal decomposition

Abstract

Based on the steady simulation results obtained by the SST k-ω turbulence model, large eddy simulation (LES) and proper orthogonal decomposition (POD) are used to examine the static pressure and vorticity modes of the wind turbine airfoil with serrated Gurney flaps (SGFs) and the baseline at α = 12° and 20°. The effect of SGF on the aerodynamic performance and radiated noise is investigated, and the influence of serration's span structure on the vorticity mode distribution is discussed. By analyzing the main modes and mode coefficients of the flow field, the mechanism of lift enhancement and noise reduction of SGF is explained. The results indicate that an airfoil with a SGF(ASGF) of 6.7%c width and 0.8%c height can effectively improve the lift coefficient within the investigated attack angles, delay stall by about 3°, and reduce the radiated noise of the airfoil by 0.51 and 4.40 dB, respectively, at 12° and 20°. Static pressure distribution analysis reveals that the SGF can significantly widen the positive pressure zone of the pressure surface, improve the ultra-low pressure regime of the suction surface, and make the pressure distribution on the suction surface more uniform, which increase the lift-drag ratio of ASGF. The POD method effectively extracts the most relevant mode of the airfoil surface radiated noise. The unsteady feature of the main flow of the airfoil is the vortices on the suction surface. The ASGF can effectively restrain the vortex separation on the suction surface and reduce the vorticity, delaying the stall and reducing the radiated noise of the airfoil surface.