Aerodynamics of vertical axis wind turbines

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Two of the main engineering limits on wind turbine utilization are power performance, particularly for smaller turbines, and aerodynamically driven vibration for both large and small turbines. The proposed research program is an investigation of the aerodynamics of vertical axis wind turbines (VAWTs). Emphasis here is on medium- and high-solidity turbines where higher solidities can be used to lower turbine rotational speeds, reducing noise and allowing better avoidance of resonance vibration. Higher solidities, however, lead to very complex flows through the turbine and around the blades, including: high blade angles of attack, dynamic stall with massive flow separation, blade-wake interactions and non-uniform diversion of the wind around the turbine. The unsteady aerodynamic loads from these flows have components that both provide turbine power and excite vibrations. My group is one of only two in the world examining vibration excitation as well as turbine power even though turbine vibration has been the main impediment to the extensive use of VAWTs. The objectives of this research program are to increase understanding of the flows around these turbines, and exploit those flows to produce lower vibration, higher efficiency turbines.*** The research program will use two approaches: wind tunnel testing and computational fluid dynamics simulations, both of which face significant research challenges. Wind tunnel testing will be done with a large 3.5 kW turbine as the behaviour of smaller models is highly dependent on their size. This research will build on my group's proven experience with turbine testing, and will benefit from our previous development of a large research turbine and associated measurement systems. Extensive computational resources must be used for the large-scale numerical simulations, which are complicated by the rotating geometry and the nature of the flows. *** The proposed research program will be the first to thoroughly investigate a range of inter-related fundamental turbine parameters, including blade aspect ratio, turbine aspect ratio and turbine solidity, and their complex and often competing aerodynamic effects. The improved physical understanding of the turbine aerodynamics will be used to exploit these findings (e.g. through asymmetric blades and the first-time application of winglets) to increase power efficiency and reduce vibration loading, which will ultimately help the implementation of VAWTs for renewable energy generation.**