Performance assessment of an innovative Gurney flap for straight-bladed vertical axis wind turbine

Abstract

Based on the vortex trapping capability of the cavity and the lift improvement mechanism for the Gurney Flap (GF), their combined impact on aerodynamic efficiency of the straight-bladed vertical axis wind turbine (SB-VAWT) was investigated. In order to eliminate the flow resistance of the blade caused by GF in the windward zone, an active flow control technique, a pivoting GF could change its position as the blades rotates in a cycle, is proposed in this paper. A grid sensitivity analysis by Grid Convergence Index (GCI) is first carried out to examine the convergence of the numerical model. Considering different GF control strategies, Computational fluid dynamics (CFD) method was used to evaluate the potential of the movable cavity-GF (c-GF) for power augmentation of SB-VAWT with traditional fixed cavity-GF. The simulation results show that power coefficient for movable c-GF is increased by more than 20% in comparison with the clean one. An appropriate active control solution not only has excellent power extraction in the downwind revolution, but also can significantly eliminate the resistance effect in the upwind zone cause by fixed c-GF. In addition, the benefits of the movable c-GF were prominent especially at the smaller tip speed ratios which indicates that it can be used for both newly designed turbines and retrofitting solutions for existing rotors.