A better insight on physics involved in the self-starting of a straight-blade Darrieus wind turbine by means of two-dimensional Computational Fluid Dynamics

Computational Fluid Dynamics (CFD) has recently provided the needed improvements in simulation capabilities that allowed enhancing the design of Darrieus wind turbines. While the performance in operating conditions has increased, poor self-starting is still one of the major drawbacks of these machines. In this study, the aerodynamics of Darrieus-turbines during start-up were investigated using a two-dimensional CFD approach. A fluid-structure interaction simulation was carried out using the ANSYS® FLUENT® solver incorporating the sliding mesh technique and enabling the rotational degree of freedom of the Six Degrees of Freedom (6DOF) solver. The issue of translating a fully-resolved flow field into lumped parameters of use to characterize the instantaneous kinematic properties of the airfoils is tackled by means of two velocity sampling methods recently proposed in the literature, i.e. the 2-PointsAverage and LineAverage methods. The results provide a clear estimation of how much the blade local absolute velocity (V∞, L) is dependent on the instantaneous tip speed ratio during the first revolutions of the starting rotor. At λ