Numerical simulation study of impact of stagger angle and radius ratio on performance of combined type VAWT

Darrieus-Savonius combined rotor could effectively improve the performance of sole type vertical axis wind turbine. In order to investigate the impacts of radius ratios and stagger angles on the combined rotor, and their best combination, aerodynamic simulations of different radius ratios and stagger angles were studied. The numerical simulation is based on 2D unsteady incompressible air model and realizable k-ε turbulence model. The result indicates that the radius ratio represents the occupied swept area of Savonius rotor, the larger radius ratio, the higher proportion of the positive momentum outputs (M≥0) in a rotation period. In addition, there exists an optimal stagger angle under a specific radius ratio making the turbine operate in higher tip speed ratio zone with maximum power coefficient.