On the Effects of a Vortex Breaker on the Wake Meandering Characteristics of a Miniature Wind Turbine

Abstract

This investigation sought to understand how the addition of a vortex breaker to the nacelle of a miniature wind turbine might disrupt, enhance, mitigate, or otherwise alter the meandering characteristics of the wake flow. Velocity measurements were taken in the wake of the turbine in a wind tunnel experiment, and analyzed with MATLAB and Microsoft Excel. Three vortex breakers were designed, and each of these cases was compared to the wind turbine with no nacelle additions. A decrease in mean streamwise wake velocity and appreciable shifts in the peak meandering frequency and intensity were observed. Peak spanwise frequencies were normalized by the mean wake velocity to compensate for effects due to increased drag on the turbine when the vortex breakers were added. This normalization is appropriate, as previous experiments have shown that wake meandering scales with the Strouhal Number (St = fD/U) for utility and small-scale turbines [1]. Meandering frequency variations between vortex breaker cases and the bare nacelle case were partially attenuated when analyzing Strouhal percent differences. This suggests that the alterations in the meandering characteristics were a combinatorial result of both increased nacelle drag and vortex interactions between the nacelle vortex and blade tip vortices.