An investigation on the aerodynamic performance of a co-axial contra-rotating vertical-axis wind turbine

In this study, a conceptual co-axial contra-rotating vertical axis wind turbine (CR-VAWT) is conceived by splitting the single conventional vertical axis wind turbine (C-VAWT) blade length into two equal lengths forming two rotors separated by a small distance about the same axis of rotation. The available literature lacks much systematic investigation to find the best possible numerical setting and to extract an in-depth understanding of dominant factors limiting the aerodynamic performance of the CR-VAWT using CFD, constitutes the primary focus for the present study. Results from the CFD were compared with the analytical model formulated using FAST along with literature results. The power output of the CR-VAWT agrees well in the low wind speed and variation increases gradually as the wind speed increases compared to C-VAWT, however, the thrust is in good agreement at all wind speeds. The wake velocity directly behind the C-VAWT and CR-VAWT follows the general trend but differences were noticed to a distance accordingly, with the wind speed. The power performance reduces gradually with increasing speed for a fixed blade pitch angle. The present adopted concept of CR-VAWT are found to have negligible aerodynamic torque and side-side force action at the tower base.