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|Title:||THE EFFECTS OF BLADE PITCH AND MOUNT POINT OFFSET ON VERTICAL AXIS WIND TURBINE PERFORMANCE|
|Keywords:||Mechanical Engineering;Mechanical Engineering|
|Abstract:||<p>Small scale Vertical Axis Wind Turbines (VAWTs) show potential for urban rooftop installations where they can capture the highly unstable, turbulent wind flow patterns which are typical in an urban environment. Being axisymmetric, they are omnidirectional turbines which respond well to changes in wind direction, unlike their horizontal axis counterparts. Wind tunnel experiments were performed on a small scale, 2.5m diameter by 3m high, 3 bladed H-Darrieus VAWT. The effects of blade preset pitch and blade mount-point offset were investigated. Local flow visualizations were observed on the inner surface of a blade near the lower strut by recording video of the behaviour of Mylar tufts during turbine operation for comparison with a 2-D Computational Fluid Dynamic (CFD) model. Experimental data is presented for a range of tip speed ratios, at a nominal wind velocity of 10m/s for both blade pitch and blade offset tests.</p> <p>The results of the blade preset pitch tests indicate performance increases with increasing toe-out pitch, to a limit, followed by a sharp decrease in performance as toe-out is continually increased. Performance decreases were experienced for all toe-in pitch presets. Identical behaviour was seen with experiments involving blade mount-point offsets which were geometrically equivalent to blade pitch presets. Results of tuft flow visualization tests indicate the regions during which the blade is experiencing reversed flow, and compare well with velocity vector data obtained from CFD simulations. The duration the inner blade surface experiences full stall is observed to decrease with the increase of toe-out preset pitch. Incipient stall is observed to be delayed as blade tip speed ratio is increased. Thrust curves are also presented and indicate a decrease in upwind pass and increased downwind pass perfonnance as toe-out is increased. As the tip speed ratio is increased, the interaction of the blade with its shed vortex from the upwind pass is diminished. This investigation shows that high solidity VAWTs are sensitive to relatively small changes in blade preset pitch and mount point offset and therefore care should be taken when designing turbine blades so as to avoid a toe-in condition that could adversely affect turbine performance.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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