Numerical investigation of Darrieus wind turbine with slotted airfoil blades

•The slotted airfoil achieves similar peak glide ratio to baseline airfoil.•The peak glide ratio of slotted airfoil covers wider range of angle of attack.•The flow separation over the slotted airfoil is delayed to an angle of attack of 20°.•The slotted airfoil VAWT has higher torque and power coefficients at lower TSR.•Static simulations showed improved starting torque of the slotted airfoil turbine. Low starting torque is considered as one of the major drawbacks of Darrieus type vertical axis wind turbine (VAWT). Design optimization to overcome this problem by modifying the airfoil geometry has received great attention by the wind energy community. Moreover, efforts have been directed towards augmenting the power coefficient of the turbine. In the present work, the effect of employing slotted airfoil as turbine blade on the performance and starting characteristics has been investigated. The slot parameters; slot location, angle of inclination, and dimensions, were optimized for NACA 0018 airfoil which is commonly used in Darrieus turbines. The flow over the turbine was modelled using ANSYS-FLUENT code. The main observations of the present study show that the VAWT with slotted Airfoil (SA) has a lower optimum tip speed ratio (TSR) compared with the Baseline (BL) turbine. This is associated with the ability to generate higher torque at lower rotational speeds. The analysis of the aerodynamic behavior of the SA turbine shows that the airfoil slot delays the separation at high angles of attack, and therefore improves the torque and power coefficient at low TSR.