Impact of rotor solidity and blade number on wake characteristics of vertical-axis wind turbines

Wake interference between wind turbines is a major concern in wind farms and is primarily driven by the wake of upstream turbines. For vertical-axis wind turbines (VAWTs), although previous studies have explored how various geometrical parameters affect their wake, three-dimensional numerical analyses regarding rotor solidity and blade number remain limited. To bridge this gap, based on high-accuracy improved delayed detached-eddy simulations, this study first investigates the impact of rotor solidity (σ) in the range of 0.12–0.6 on the wake characteristics of three-bladed VAWTs. Then, the wake fields of two- and three-bladed VAWTs with the same solidity are compared. The results show that the increased σ leads to larger wake widths, stronger wake asymmetry, larger velocity deficits in the near wake region, and faster wake recovery in the moderate and far wake regions. From the perspective of building efficient wind farms, a lower σ (e.g., 0.12) is suggested if the turbine spacing is relatively small (e.g., 2 D, where D is the rotor diameter), while a higher σ (e.g., 0.48) is more favorable for a larger turbine spacing (e.g., 7 D). With decreasing blade number, the strength and instability of the tip vortices increase, which promotes vortex dissipation and shear layer destabilization, resulting in smaller wake widths and faster wake recovery in the vertical plane. For a relatively high σ, the two-bladed design benefits the downstream turbine performance. These findings support the selection of turbine geometries in designing wind farms.