Abstract
This experimental work describes the effect of protuberances at the trailing edge of the blades of a three straight bladed cross-flow turbine. The performance of the turbine was studied after wind tunnel experiments and results are compared against a turbine with the same characteristics but having blades with symmetric profiles.
The turbine model was based on blades with NACA-0015 profile, with a chord-to-diameter ratio of 0.16. The especially designed set-up included measurements of the shaft torque and speed, as well as the characterisation of the incoming wind profile. The model had a fixed pitch angle of 6 degrees toe-out and the blades were designed to allow easy interchangeability of the trailing edges. The different trailing-edge bumps investigated resulted from combinations of sinusoidal functions with wavelengths of 0.250 and 0.125 times the blade chord, with amplitudes of 0.005, 0.010 and 0.015 times the chord. The tip speed ratios covered in these wind tunnel experiments go up to 2.4 at a fixed Reynolds number near 4·105.
The results show evident changes in the performance of the turbine. These are believed to be caused by the protuberances, inducing the development of a secondary flow pattern in the spanwise direction of the blade. This would modify the blade-wake interactions inside the rotor, and therefore the overall performance.
