Wind tunnel tests on a straight-bladed vertical axis wind turbine

Abstract

The Straight-Bladed Vertical Axis Wind Turbine is a machine which has received scarce attention until recently. This turbine can offer high efficiencies at minimal construction and maintenance costs. This type of turbine extracts energy from the wind by virtue of the dynamic reaction of the air on the rotor blades and as such most of the factors which influence the rotor's efficiency are related to the blades. As such, in establishing a set of performance curves for this type of wind turbine the effects of altering blade pitch and blade chord were investigated. For this purpose a model with balsa wood blades, 0.21m in diameter, was constructed. The model allowed a number of pitch offsets and blade chords to be tested, at various Reynolds Numbers, in the Wind-Tunnel at the University of Malta. The test results were presented in the form of Power and Torque Coefficient as functions of Tip Speed Ratio. They were obtained by measuring the shaft torque, the rotor's rotational speed and the condition of the air entering the test-section of the Wind-Tunnel. During the tests the Reynolds Numbers investigated varied between 176000 and 236000. The range of tested pitch offsets was -4° to +4. Because of the small size of the model only two chord values could be tested.