Aerodynamic optimization of a vertical axis wind turbine equipped with a two-element airfoil

The results for the optimization of the Darrieus rotor equipped with a slat airfoil are presented. The problem appears to be well defined with respect to the adopted optimization routine and decision variables. These independently provide the maximum performance for a given value, which was correctly included in its range of variation. The physical reasons behind the optimal slat airfoil position are linked to the rotor aerodynamics, given the increase in the main airfoil operative range which is obtained by introducing the secondary airfoil. Moreover, the analysis of the parameters such as the slat airfoil pitch angle and chord length highlighted a variation in the optimal operating conditions in the considered range. Depending on the slat characteristics, in fact, the aerodynamic effect is enhanced for different angles of attack and, therefore, different tip speed ratios. The maximum performance is however achieved for a particular operating condition which is maintained along the optimization process.