The Darrieus wind turbine is a type of vertical-axis wind turbines which, in spite of its simple structure, is very complex to analyze. In terms of aerodynamics, Darrieus VAWTs have properties which tend to make them distinctive of horizontal-axis wind turbines but generally are less effective. In the present research, a cavity is created into blade's profile of a VAWT to enhance its performance. The computational fluid dynamics have been used to simulate the turbine in turbulent flow and finally calculate the forces affecting it. The shear stress transport (SST) k-w turbulence model has been used to complete the governing equations and the turbine has been modeled in two dimensions. In order to enhance efficiency and aerodynamic performance of the turbine, effects of different dimple parameters including diameter, profile and its location has been considered. The optimum airfoil state has been found with circular dimple with diameter equal to 8% of cord length located on pressure side of the airfoil and near the leading edge. Eventually, it was observed that the efficiency at optimal performance (l ¼ 2.6) and average efficiencies of the turbine were 18% and 25% improved when using the airfoil with a cavity, as compared to the reference airfoil.

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