Investigation of fundamental mechanism leading to the performance improvement of vertical axis wind turbines by deflector

Wind energy utilization in urban areas revives the interests in vertical axis wind turbine (VAWT). An upstream deflector has demonstrated to increase the overall efficiency of two closely spaced VAWTs more than 30% in previous experiment research. However, the optimal geometrical configuration and the mechanisms driving the performance improvement have not been fully investigated. In this study, a parametric investigation is conducted to obtain deeper fluid-mechanical insights into the interactions between two VAWTs and the deflector. The instantaneous blade load, averaged rotor torque coefficient, and near-field flow are obtained in different layouts to assess the wind turbine aerodynamic performance. The numerical results show that the blade experiences a larger relative velocity and favorable angle of attack under the influence of a deflector. There is an optimal configuration for the two wind turbines with a deflector, which increases the maximum torque coefficient by 23% relative to the configuration without a deflector. The use of the deflector affects the wake recovery to a location downstream in comparison with the no-deflector setup. Furthermore, the performance of the twin VAWTs is sensitive to the wind directions. In the skewed incoming flow, the twin VAWTs still have a better performance under the influence of a deflector.