Design of a Retractable Vane for a Vertical Axis Wind Turbine

This study investigated the impact of vane design for a retractable vane Savonius style Vertical Axis Wind Turbine (VAWT). Five designs were tested in a wind tunnel to find which design produces the most torque on the rotor, and to obtain a value for drag coefficient and lift coefficient. Eight position angles were selected to represent the infinite number of vane positions possible compared to the direction of the wind. The wind tunnel was not able to generate air speeds great enough to reach the Reynolds numbers (Re) required for similarity. Reynolds number independence was sought to justify extrapolation to the required Re. In many cases extrapolation was not reasonable. Instead the data was analyzed assuming a “best approximation” range for each vane and position. The testing setup introduced extra uncertainty that was considered in analysis, and presumed to be harmonic motion of the setup and/or the evidence of vortex shedding. The best vane design proved to be an airfoil with a curved trailing edge, although all designs proved feasible for power production. The curved airfoil design reduced possible vortex shedding and the induced drag to become the most consistent, high torque producer of the five designs. The net torque seemed to be influenced more by the vane position than the vane design. Thus, more importance may lie in the design of the retraction mechanism than in the vane design. With this curved airfoil design, research can extend to a study of retraction mechanisms, power production systems, and, eventually, construction