Effect of bearing dissipative torques on the dynamic behavior of H-Darrieus wind turbines

In recent years, the study on wind turbines for electricity generation has achieved significant advances in the development of new formulations, analysis or even in efficiency. The growth in the use of wind technologies comes from two main facts: (i) utilization of renewable energy sources, and (ii) as an alternative solution to the existing global potential. Hence, vertical-axis wind turbines (VAWTs) present, among other advantages, the possibility of greater efficiency at low tip speed ratios, mainly compared to the horizontal-axis ones. Additionally, the possibility of receiving flow from any direction without the need of tail assembly. As disadvantages, VAWTs present difficult in starting shaft rotation from the rest, being it even more perceptible in small wind turbines, as the drivetrain resistance is relevant. In this sense, this work aims to study the effect of bearing dissipative torques on the dynamic behavior of a H-Darrieus (straight-bladed Darrieus) wind turbine. An approach adding bearing resistance torques is proposed considering their influence on the final rotational speed of the rotor turbine. The proposed method is based on the Newton’s second law, with the torque generated by the turbine and the forces acting on the bearings provided by the double-multiple streamtube model. Bearing dissipative torques are calculated using two methodologies. A correction of those methodologies, in order to consider the Stribeck effect, is also implemented. The results of the model are compared with data from the literature, demonstrating good physical consistency.