Investigation of V-shaped blade for the performance improvement of vertical axis wind turbines

The vertical axis wind turbine (VAWT) is regarded as an important device to utilize the renewable offshore wind energy to supplement the existing power systems. Hence, the demand for higher wind energy conversion makes the research focus on the blade optimization of wind turbines. This paper attempts to propose a novel VAWT structure with V-shaped blade to improve the power outputs at moderate tip speed ratios. The feasibility of the Reynolds-Averaged Navier-Stokes SST kappa - omega turbulence model applied on the VAWT was verified against available experiments at first. Then a comprehensive investigation on the aerodynamic performance of such V-shaped VAWT was carried out using the SST kappa - omega model. The results indicated that the maximum enhancement in power coefficient obtained in the optimal V-shaped blade was about 24.1%. In addition to the great improvement of the power efficiency, the V-shaped blade was proven to alleviate the damage caused by lateral loads to the wind turbine. Besides, the flow structures over the blade surface were studied to reveal the mechanism of dynamic stall with the reason of power increase explained. Moreover, it was found that the V-shaped blade could effectively suppress the flow separation and delay the dynamic stall in the middle of the blade, and the undesirable blade tip effect would not be more serious comparing to that of the conventional straight blade. It was finally concluded that the current work could be practically applied to the design and optimization of the VAWT blades.