Aerodynamics of a Small-Scale Vertical-Axis Wind Turbine with Dynamic Blade Pitching

Abstract

This paper describes the systematic experimental and computational studies performed to investigate the performance of a small-scale vertical-axis wind turbine using dynamic blade pitching. A vertical-axis wind turbine prototype with a simplified blade pitch mechanism was designed, built, and tested in the wind tunnel to understand the role of pitch kinematics in turbine aerodynamic efficiency. A computational fluid dynamics model was developed, and the model predictions correlated well with test data. Both experimental and computational fluid dynamics studies showed that the turbine efficiency is a strong function of blade pitching amplitude, with the highest efficiency occurring around to amplitude. The optimum tip-speed ratio depends on the blade pitch kinematics, and it decreases with increasing pitch amplitude for the symmetric blade pitching case. A computational fluid dynamics analysis showed that the blade extracted all the power in the frontal half of the circular trajectory; however, it lost power into the flow in the rear half: one key reason for this being the large virtual camber and incidence induced by the flow curvature effects, which slightly enhanced the power extraction in the frontal half but increased the power loss in the rear half. The maximum achievable of the turbine increased with higher Reynolds numbers; however, the fundamental flow physics remained relatively the same, irrespective of the operating Reynolds number. This study clearly indicates the potential for major improvements in vertical-axis wind turbine performance with novel blade kinematics, a lower chord/radius ratio, and using cambered blades.