Parametric Design of Radial Guide Vanes for Power Augmentation of Darrieus-Type Vertical-Axis Wind Turbines

Among proposed solutions for power augmentation of Darrieus turbines, one of the most promising is represented by Radial Guide Vanes (RGVs) which can potentially increase both the velocity magnitude and the swirl of the incoming flow, without losing omni-directionality like in the case of diffusers. The main drawback of this technology is the increase in the dimension of the wind energy converter, which however comes together with reasonable cost (only static parts are added) and additional benefits like a higher safety and lower noise. The study presents an extensive parametric analysis aimed at investigating the impact of some key design parameters of a RGV cascade on the performance of a medium-size industrial Darrieus rotor. Focus is given to vanes angle and length. Simulations are carried out by means of the two-dimensional Actuator Line Model developed by some of the authors for the commercial ANSYS® FLUENT® 20.2 solver. The hybrid simulation approach has been validated against blade-resolved unsteady CFD RANS simulations of the machine in both open- and vaned-rotor configurations. The use of high-fidelity techniques comes indeed with a non-negligible calculation cost, but it can solely provide the needed accuracy in modelling the physics related to the interaction of the flow with both static and rotating blades. Different turbine operating points and inlet flow angles are considered, so that the effective omni-directionality of the RGV concept could be verified. Tested configurations are compared in terms of power coefficient and blade loading azimuthal profile. Overall, results prove that — if the correct design is chosen — RGVs can provide notable improvements in the performance of a Darrieus VAWT, opening interesting prospects for their future application in industrial installation.