Utilization of guide vanes to concentrate flows to the blade and block vortex to improve the power factor of savonius wind turbine

Abstract

Simple design Savonius vertical-axis wind turbine can generate energy at low wind speed from any direction. However, its large static torque has a low power factor. Therefore, an innovation was made by providing 16 guide vanes around the shaft outside the blade with the angle is about 45° to a radial line. The specialty of guide vanes is that , they are able to concentrate the wind flow toward the turbine blade from any direction. The fluid motion around the turbine blade that produces torque on the turbine shaft was analyzed utilizing the Computational Fluid Dynamics (CFD) simulation and then verified by tracking actual fluid motion strings of threads attached on each side of the turbine blade. The result shows that without guide vanes the wind flow around the turbine blade generates vortex on the blade and Karman vortex at the downstream. These vortexes descend effectively kinetic energy in the wind flow so that the mechanical energy on the turbine shaft becomes small. At a certain blade position, the vortex becomes stronger and the fluid separation from the blade surface becomes thicker. The stronger vortex tends to descend stronger fluid kinetic energy while the thicker separation tends to reduce the lift on the blade. Consequently, these two flow conditions tend to produce negative torque. Installing guide vanes around the blade, the wind flows are concentrated by the guide vanes to the turbine blade, which effectively reduces vortex around the blade and blocks large vortex outside the guide vanes downstream. Flow separation is suppressed by the concentrated flow producing larger lift. As a result, the power factor increases by 61.6 %. This huge increase in power factor is achieved when the wind speed is 5 m/s though a stable turbine rotation is achieved at a lower speed