Impact of Wind Turbine Rotor Blade Bound Circulation Distribution on Wake Diffusion

Abstract This study investigates how variations in circulation distribution along the rotor blades of horizontal-axis wind turbines influence downstream wake development. Turbines operating in the wake from upstream turbines experience reduced power output, decreasing the overall annual energy production (AEP). To mitigate this effect, wind turbine rotors can be designed to promote wake diffusion, increasing energy availability for downstream turbines and enabling closer turbine spacing in wind farm layouts. Using the NREL-5MW turbine as a reference, five alternative rotor designs with modified twist angle distributions are examined to control circulation and its impact on wake characteristics. Two of these designs, inspired by patents from Equinor and the Sandia National Laboratories (SNL), aim to enhance wake diffusion. Additionally, two rotors are analysed with overall lower and higher aerodynamic loading across the blade span. A fifth rotor is introduced, featuring a modified bound circulation distribution induced by targeted twist angle adjustments to generate stronger vortex structures in the wake. The twist angle distribution of the NREL-5MW reference turbine is adjusted using Bézier-based scaling curves applied within a suitable parameter space. The wake development is analysed using a vortex particle method. An analysis of the wakes’ vorticity and mean velocity indicate that Equinor ’s rotor concept achieves the most effective wake diffusion while maintaining relatively low power losses at the rotor.