Abstract
VAWT such as the Darrieus turbine, could effectively be used in urban spaces. However, the poor self-starting of this type has been considered as a major drawback which limits its application. This also hinders the turbine’s operation at low wind speeds. While the wind energy research community have been lately focusing on augmenting the power coefficient of the Darrieus machines, the enhancement of self-starting capabilities has not attract much attention. In this research, some modifications were applied to the Darrieus type VAWT blades in order to improve its self-starting capability. This entails the application of slotted and Gurney flapped airfoils. The proposed modifications were tested using computational fluid dynamics (CFD) tools. The commercial software ANSYS FLUENT© was used to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) in two dimensions, using two different techniques: the first one is by setting a constant rotational speed for the turbine, and the second one is using the Six Degrees of Freedom (6DOF) solver to calculate the rotational speed during starting due to generated aerodynamic torque on the blades. The proposed airfoil modifications using slot and Gurney flap were applied on Darrieus type VAWT. In a previous study by the authors, the slotted airfoil was shown to enhance the starting torque capabilities, however, the maximum power coefficient decreased, compared to the baseline airfoil turbine. Adding the Gurney flap to the slotted airfoil shows a significant enhancement of the power coefficient throughout the operating range of the turbine. Moreover, the maximum power coefficient of the proposed turbine is also higher than that of the baseline turbine. Further, the self-starting capabilities of the slotted-flapped airfoil turbine has also been remarkably augmented compared to the baseline turbine.
