Reynolds Number Effect on the Optimization of a Wind Turbine Blade for Maximum Aerodynamic Efficiency

Abstract

Because of the increase in wind rotor size, the Reynolds number of an airfoil profile can reach a very high value. The effect of the Reynolds number on the aerodynamic performance of airfoils is investigated, and its influence on the optimal design of a wind rotor aiming to maximize the power coefficient is discussed. Six airfoils are involved—four DU and two NACA6—as well as five Reynolds numbers varying from 106 to 107, which cover most commercial wind turbines. At a higher Reynolds number, all of the airfoils exhibit better performance, such as a higher lift coefficient, a lower drag coefficient, and a larger lift-to-drag ratio at a given angle of attack. The largest lift-to-drag ratio and the corresponding lift coefficient and angle of attack also change with the Reynolds number, which in turn affects both the performance and the optimal shape of a blade. The results show that a practical blade operating at a higher Reynolds number requires a duller shape with a greater twist angle, and has a better power coefficient than those operating at lower Reynolds numbers.