Scale Effects on Vertical Axis Wind Turbines Aerodynamic Performance and Flow Characteristics

Abstract

Reynolds number is important to distinguish flow characteristics between large-scale and small-scale wind turbines. Dimensional analysis shows that scaling wind turbine as a whole only results in a change in Reynolds number, while other dimensionless variables affecting the flow features, such as solidity and reduced frequency, remain unchanged. Thus, a univariate analysis of scale effects can be achieved in this way. This paper first derived the relationships between wind turbine scale and Reynolds number, solidity, and reduced frequency. A series of high-resolution numerical simulations were then performed for a simplified single-bladed vertical axis wind turbine model with the Reynolds number varying from 1×10⁴ to 5×10⁶, while keeping the other two parameters unchanged. The results show that over the range of Reynolds number investigated, as the scale of wind turbine increases, the flow separation nearby the blade decreases, the strength of the dynamic stall vortex becomes weaker, and the power coefficient generally tends to increase. Specifically, in the range of 5×10⁴ ≤ Re c  ≤ 5×10⁵, the power coefficient increases significantly as the scale of wind turbine increases, while in the range of 5×10⁵ ≤ Re c  ≤ 5×10, the power coefficient still tends to increase, but in a decreasing increment.