A Novel Blade-Pitching Mechanism Design and Testing for Micro Vertical-Axis Water Turbines

Abstract

This paper deals with improving the power output of a vertical-axis water turbine by controlling blade pitch-angle. During turbine rotation, the angle-of-attack of the blades varies at each azimuthal location due to constantly changing relative velocity. In the case of the H-rotor vertical-axis water turbines, the output torque is lift-dependent. The constantly changing angle-of-attack results in sub-optimal lift generation. Hence, the output torque (or the turbine power output) is compromised. This script introduces a novel design for controlling the turbine blade pitch-angle. The new design increases the overall lift-force produced by each blade during each azimuthal rotation cycle.  The design incorporates a novel sun-planetary gear mechanism to control the blade pitch-angle continuously, to maintain a constant pre-set angle, with the incoming flow velocity. This improves the blade angle-of-attack by limiting angle variation to ±90o from the ±180o variation experienced by fixed blade turbines, during its rotation cycle. This results in better lift generation. The experimental results show that the proposed design substantially increases the amount of flow kinetic-energy harvested by the turbine, providing up to a 38.5% increase in turbine power output.