CFD simulation of the aerodynamic performance of co-axial multi-rotor wind turbines using the actuator line method

Multi-rotor wind turbines (MRWTs) have attracted widespread attention due to their high efficiency and large generating capacity, and they have become a potential solution for offshore wind turbines. A co-axial MRWT has the advantages of high power density and a small footprint. The actuator line method-large eddy simulation (ALM-LES) is applied to investigate the aerodynamics and near-wake characteristics of unidirectional and counter-rotating co-axial MRWTs. The influence of the blade tip vortices on rotor-to-rotor interactions, wake mixing, and recovery are analyzed. The results show that the unidirectional co-axial twin-rotor wind turbine has a good aerodynamic performance. The torque of the two rotors fluctuates significantly and periodically when the twin rotors rotate in reverse. A distance of 0.3 R between the rotors causes the front rotors to impact the aerodynamic performance of the rear rotors, whereas exceeding 0.5 R minimizes the influence of the rear rotor on the front rotor. And an appropriate azimuth angle should be selected to avoid adverse effects on aerodynamic performance.