Effect of chord-to-diameter ratio on vertical-axis wind turbine wake development

The wake structure of a vertical-axis wind turbine (VAWT) is strongly dependent on the tip-speed ratio, λ , or the tangential speed of the turbine blade relative to the incoming wind speed. The geometry of a turbine can influence λ , but the precise relationship among VAWT geometric parameters and VAWT wake characteristics remains unknown. To investigate this relationship, we present the results of an experiment to characterize the wakes of three VAWTs that are geometrically similar except for the ratio of the turbine diameter ( D ), to blade chord ( c ), which was chosen to be D / c = 3, 6, and 9. For a fixed freestream Reynolds number based on the blade chord of R e c = 1.6 × 10 3 , both two-component particle image velocimetry (PIV) and single-component hot-wire anemometer measurements are taken at the horizontal mid-plane in the wake of each turbine. PIV measurements are ensemble averaged in time and phase averaged with each rotation of the turbine. Hot-wire measurement points are selected to coincide with the edge of the shear layer of each turbine wake, as deduced from the PIV data, which allows for an analysis of the frequency content of the wake due to vortex shedding by the turbine.