VAWT in double-rotor configuration: the effect on airfoil design

This work presents a study to identify the effect of double-rotor configuration on the airfoil selection of vertical-axis wind turbines (VAWTs). Simulations are performed using an inviscid panel/vortex model for two different counter-rotating layouts (counter-up and counter-down) and various tip speed ratios, solidities and rotor spacings are considered. The double-rotor configuration relatively enhances the power production and the flow characteristics revealed that this is due to the wake contraction, flow acceleration, and favourable angle of attack in between the rotors. With a multi-objective optimisation scheme airfoils are designed by balancing the aerodynamic and structural needs. The optimised airfoils outperform the airfoils from the initial generation and show the importance of an appropriate airfoil selection. The angle of attack encountered by the turbine in double-rotor configuration is only effected noticeably in between the rotors and therefore it is concluded that the double-rotor configuration does not significantly influence the airfoil design.