Design of twist-modified lab-scale wind turbine rotors for enhanced wake recovery

Abstract Enhancing power production in wind farms by improved wake recovery has emerged as a major research focus in recent years. By implementing flow control strategies on turbine rotors, researchers aim to mitigate wake effects and optimize energy output across entire wind farms. The wake-diffusion rotor concept proposed by Equinor deviates from traditional rotor designs by modifying the blades’ radial twist angle distribution. The loading on the inner portion of the rotor blades is intentionally decreased to create additional flow entrainment and shear gradients in the center of the wake. To investigate this, performance and wake flow experiments are conducted on three rotor blade sets, two featuring moderate and radical twist angle modifications, respectively, in a lab-scale experimental campaign. In both cases the inner half of the blades’ radius is de-loaded. The three rotors are mounted to a underwater test turbine equipped with both torque and thrust sensors for performance measurements. The three-dimensional flow field in the wake is captured using a Lagrangian Particle Tracking Velocimetry (LPTV) at several downstream distances of the rotors. Results from initial power and thrust measurements show only minor differences in the three rotors’ power output at their design tip speed ratio. A comparison of the mean components in the wake indicates an improved wake recovery for the two modified rotors. In the near wake the wake diffusion rotors show locally higher mean velocities in the wake center, where additional wake diffusion is initiated. These initial results indicate a promising potential for the concept, while measurements under various inflows and at larger downstream distances are needed to quantify the full potential.