Effect of rotor spacing, overlapping and non-overlapping, on the performance of a coupled counter-rotating twin-rotor VAWT using CFD

The aim of present study is to do an assessment of the performance of the counter-rotating coupled twin-rotor VAWT using NACA0018 blades. When overlap is present (i.e., the distance between the rotor hubs is less than the rotor diameter) the rotors are coupled together such that the blades are staggered at a fixed phase. Additional studies are also undertaken for the twin-rotor configuration where there is no overlap in their path of motion. A 2D URANS CFD study was undertaken after validation on the standard single H-rotor VAWT. The simulations were carried out with the twin-rotor VAWT for the same governing conditions and flow parameters utilising the overset mesh approach. It is observed that, at the optimal overlap, each rotor of the coupled counter-rotating twin-rotor design produces a higher power output compared to the single-rotor VAWT by 25 %. This enhanced performance can be attributed to constructive aerodynamic interference between the overlapping rotor blades as well as the acceleration of the flow in the overlap region. Overall, the twin-rotor VAWT has good potential in wind farms both on land and offshore.