Abstract—A numerical study was carried out to investigate the effects of a Gurney flap on the aerodynamics performance of the NACA 0018 aerofoil and an associated three-blades rotor of a H-type Darrieus wind turbine. The flow fields around a single aerofoil and the Vertical Axis Wind Turbine (VAWT) rotor are studied using URANS. The height of Gurney flap ranges from 1% to 5% of the aerofoil chord length. The flow fields around a single aerofoil and the Vertical Axis Wind Turbine (VAWT) rotor are simulated using URANS. The results show that the Gurney flap can increase the lift and lift-to-drag ratio of the aerofoil. As a result, adding a Gurney flap can significantly improve the power coefficient of the VAWT at low tip speed ratio, where it typically gives low power production. The causing mechanism is discussed in detail