Investigation of helical Darrieus turbine wake using actuator line model–large Eddy Simulation approach: Wake recovery and energy redistribution

This work presents an analysis of wake dynamics of vertical-axis wind turbines (VAWTs), employing the actuator line model in conjunction with large eddy simulation. Three turbine configurations—a straight-bladed turbine and two helical-bladed turbines with 90° and 180° twists—are investigated under a tip-speed ratio of 4.5 for the turbulence intensity of 0.5% and 5%. This study focuses on quantifying wake recovery mechanisms, turbulence characteristics, and energy redistribution using velocity fields, transport mechanisms, and modal decomposition. The results show that increasing the helical angle leads to earlier vortex breakdown, shorter near-wake regions, and faster streamwise velocity recovery. Helical turbines induce significant vertical velocity components and exhibit enhanced lateral and vertical turbulent transports, which accelerate wake mixing. Proper orthogonal decomposition analysis reveals that the first mode captures more than 99% of the streamwise energy in all cases, while energy distribution across higher modes increases with helical angle, especially in the vertical component. This redistribution is attributed to reduced dynamic stall intensity in the helical configurations. Furthermore, a shift in the dominant frequency of the temporal modes indicates that vortex shedding becomes less intense and more spread out with increased blade helicity. The findings highlight the aerodynamic advantages of helical VAWTs, particularly in enabling denser turbine arrays.