Development and Validation of a Hybrid Simulation Model for Darrieus Vertical-Axis Wind Turbines

The increasing interest in deep-water floating applications and in wind turbine installations in turbulent flows, is putting vertical-axis wind turbines back again in research agendas. However, due to the lack of activities in past years, the accuracy and robustness of available design tools is much lower than the corresponding ones for horizontal-axis rotors. Moving from this background, the study presents the development of a hybrid simulation model able to simulate H-type Darrieus turbines with low computational effort and an accuracy higher than that of conventional low-fidelity models. It is based on the coupling of unsteady RANS CFD with the Actuator Line theory to replace the airfoils. The present tool has been implemented within the commercial solver ANSYS® FLUENT® and it is then of practical interest for a large number of potential users. With respect to other examples in the literature, the present approach includes some new findings in the correct manipulation of airfoil polars that notably increased its accuracy. The validation of the model is assessed by means of two different study cases featuring a simplified 1-blade rotor and a real 3-blade turbine, for which both detailed CFD simulations and experiments were available. The model was able to produce accurate results — both in terms of aggregate power production and of flow field description — for turbines with a medium-low chord-to-radius ratio and the tipspeed ratios typical of turbine operation.