Abstract
An experimental study is presented on the performance of a vertical axis wind turbine with variable blade geometry of the design developed by Austin Farrah. This is experimentally compared with the performance of a correspondingly sized Bach-type Savonius turbine using the same electrical generator and measurement instrumentation in a wind tunnel. Experiments were performed for Reynolds numbers, based on blade chord, in the range 5 × 103to 1 × 105, and for blade settings between −40° and +40o. The study shows that for the tip speed ratios that have been investigated, the Farrah vertical axis wind turbine design can only marginally outperform a corresponding two-bladed Bach-type Savonius turbine and then only when its blades are set to 40° pitch angle. The presence of a small inner cylinder, which rotates with the turbine, does not enhance its performance due to the fact that it is immersed in an extensive column of relatively static air.
Highlights
This article presents the results of a study to assess the performance characteristics and relative merits of the vertical axis wind turbine (VAWT) design developed and patented by Austin Farrah (1996)
The data obtained were compared to provide a detailed assessment of the performance merits of the Farrah turbine and in particular assess the effect of blade pitch setting and the size of the inner cylinder on its performance in comparison with the reference Savonius turbine
It can be said that the observed changes in turbine performance are solely due to the impact on turbine spin rate from changes to the aerodynamic forces and torques acting on the turbine and are not associated with fluctuations in generator output over time
Summary
This article presents the results of a study to assess the performance characteristics and relative merits of the vertical axis wind turbine (VAWT) design developed and patented by Austin Farrah (1996). This design comprised a number of pitchable rotor blades with aerofoil section positioned in a ring around a central circular sectioned inner cylinder, as illustrated in Figure 1 where the red line is the circumference of the undeployed blade array. With their relatively high level of peak aerodynamic efficiency, HAWT designs are generally preferred for industrial scale wind energy extraction. For smaller scale energy generation and applications, such as water pumping, VAWTs can be considered and have the benefits of being cheaper to construct and maintain, produce less noise due to their lower tip speeds, are less sensitive to wind direction and do not suffer gyroscopic effects on the rotor
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