Systematic investigation of effect of rotor solidity on vertical-axis wind turbines: Power performance and aerodynamics analysis

Small-scale vertical-axis wind turbines (VAWTs) are receiving growing interest for applications in urban areas. However, the unsatisfactory power performance, mainly induced by the complex blade aerodynamics, restricts their development. Optimizing the turbine geometry is expected to improve the blade aerodynamics. In the present study, the effect of rotor solidity on the power performance and aerodynamics of VAWTs is systematically investigated using high-fidelity improved delayed detached-eddy simulations. A wide range of rotor solidity from 0.12 to 0.6 is studied for VAWTs with different numbers of blades, i.e., two- and three-bladed VAWTs. Also, different rotor diameters (0.5 m-2 m), covering VAWTs from domestic to building integration, are compared to explore the scale effect. In addition, the Reynolds number effect induced by the change of turbine geometry is considered and its impact on the solidity effect is elucidated. The results show that a low to moderate rotor solidity (e.g., lower than 0.3) allows the VAWT to achieve appreciable peak power performance. When the inflow velocity is fixed, for a given relatively low rotor solidity (e.g., 0.12), the two-bladed design is expected to achieve higher peak turbine power, while the three-bladed design is more advantageous when the rotor solidity is relatively high (e.g., 0.36). For a given rotor solidity, VAWTs with smaller rotor diameters perform relatively better due to the diminished tip loss effect. The effects of number of blades and rotor diameter are strongly affected by the variation of the chord-based Reynolds number. This study would support the optimal design of urban VAWTs.