Improving Safety and Performance of Small-Scale Vertical Axis Wind Turbines

Although horizontal axis wind turbines (HAWT) are considered more efficient in operation than their vertical axis wind turbine (VAWT) counterpart and are more commonly used in wind farms as large wind turbines, the VAWT may offer greater advantages in safety and operation when it comes to their application within the urban environment. Yaw control systems are an essential requirement for the safe operation of HAWT, which are costly and require high levels of maintenance, but are inherently unnecessary for VAWT. At low blade speed ratios, the performance of VAWT degrades owing to strong dynamic stall effects. This necessitates VAWT operation at high blade speed ratios to suppress them. However, the consequent large rotational speeds lead to hazardous operation especially in confined urban areas. Thus to improve the low blade speed performance, a preliminary experimental investigation has been carried out at the Aerodynamics Laboratory of the University of New South Wales on an H-type VAWT blade that employed zero-net mass flux actuation. This technique has traditionally been used for static stall delay and flow separation mitigation on aircraft wings. In the present study, large relative angles of incidence were simulated by sinusoidally oscillating the blade about its quarter-chord, and resulted in the formation of dynamic stall vortices. The application of zero-net mass flux actuation was found to have a beneficial effect on the blade aerodynamic performance by either suppressing dynamic stall or delaying its onset to higher angles of attack. This study, therefore, suggests that reduced oscillatory loads and more robust output power can be achieved with zero-net mass flux actuation on VAWT operating at low blade-speed ratios. Consequently, the findings have positive practical implications for the design of small-scale VAWT for widespread use in the urban environment.