Hydrodynamics and wake flow analysis of a Π-type vertical axis twin-rotor tidal current turbine in surge motion

Abstract

For a floating tidal current turbine power station, the motion response of the floating carrier would affect the hydrodynamic performance of the tidal current turbine. To study the turbine loads and power output characteristics of the proposed twin-rotor turbine in moving condition, the hydrodynamic performance of a vertical axis twin-rotor turbine in surge motion is thoroughly discussed in this manuscript. Based on the moving mesh and sliding mesh technique, the rotary motion and surge motion of the turbine are combined to simulate the turbine operation conditions in waves and currents. The twin-rotor turbine working at different surge frequencies, surge amplitudes, and tip speed ratios is simulated and the simulation results are compared with the fixed turbine in an uniform flow. The change characteristics of thrust force, lateral force, and flow field are analyzed. The results show that the twin-rotor can improve the power output efficiency better than a stand-alone turbine. Surge frequency and surge amplitude have very little influence on the average power output of the turbine. The fluctuation amplitude of the thrust and lateral forces of a twin-rotor turbine is larger than the stand-alone turbine, while the fluctuation amplitude of thrust and lateral forces increase with surge amplitude and frequency. Spectra of turbine loads and power output show that surge and rotation frequencies have different impacts on the dynamics and performances of the turbine. The research results can provide a reference for the development of floating tidal current power stations in the future.