Exploring the Effect of Tubercles on Vertical Axis Wind Turbine Performance

Abstract

It is hypothesized that the tubercles on the humpback whale fin allow them to perform aerodynamic maneuvers, despite their size. Previous studies indicate that adding tubercles to horizontal axis wind turbine blades potentially improves post-stall lift and drag profiles, depending on the Reynolds number of the flow. This report seeks to add to the literature on tubercle performance, by investigating the performance of vertical axis wind turbine blades with added tubercles. To investigate the effects, an optimized tubercle pattern is added to a straight-edge blade, and the blades are tested in a wind tunnel using the particle image velocimetry (PIV) method. Profiles of the flow field for the tubercle blade and the unmodified straight-edge geometry obtained from the PIV data are compared to ascertain any performance changes induced by the tubercles. Comparing the wake generated by a turbine equipped with straight leading-edge blades and one with tubercles on the leading edge, the addition of the tubercle pattern on a vertical axis wind turbine is shown to decrease the velocity deficit in both the near- and far-wake as well as the spreading of the wake in the direction normal to the freestream flow. These results indicate that the tubercle leading-edge blades mitigate kinetic energy loss in the wake of the turbine. There was, however, a significant difference in the normalized power output between the two turbines, thus a conclusion about overall performance cannot be made at this time.