Twin-rotor wind turbine wake characteristics under various configurations and states

The twin-rotor wind turbine, as a new concept, can effectively improve the power coefficient, accelerate wake recovery, and reduce the cost of floating platforms and mooring compared to single-rotor turbines. This paper investigates the power and wake of tandem and parallel twin-rotor arrangements, setting up four different calculation models: vortex lattice (VL) to vortex filament conversion, different arrangements, extended blade root length, and altered initial azimuth angle. Changes under different tip speed ratios, steady and unsteady, and motion states were studied. The study found that for power and wake research, the vortex lattice calculation distance needs to be set to more than 2D and 5D (D is the rotor diameter). In the unsteady state of parallel twin-rotor wind turbines, the power coefficient difference between the two rotors is significant, and with increased turbulence intensity, the spacing ratio should be appropriately increased, with an optimal choice existing. For tandem twin-rotor arrangements, the initial staggered arrangement has little impact on power but significantly affects the wake. Increasing the length of the circular airfoil section of the blade root can effectively improve the power of the smaller rotor without changing the power coefficient of the larger rotor. Applying sinusoidal six degrees of freedom motion to the twin-rotor wind turbine can increase the power coefficient except for yawing. This research is of great significance for the arrangement of twin-rotor, reducing floating platform costs, and optimizing wind farm layout.