Abstract
Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.
Highlights
For the effective utilization of wind energy, various research and development activities such as floating offshore wind power generation using largescale wind turbines and wind environment assessment
In order to investigate the effect of blade camber direction and pitch angle on the performance of a small-scale straight-blade Darrieus vertical axis wind turbine (VAWT) with symmetrical NACA0018 airfoils, the numerical analysis of the single NACA0018 airfoil with/without the Gurney flap and the performance tests of the VAWT test model by using the Gurney flaps were conducted
1) Numerical analysis of single NACA0018 airfoil with the Gurney flap used in the VAWT test model shows that the Gurney flap can improve the lift characteristics even in the low Reynolds number region, and ΔCL ave = 0.42 at h/c = 0.036 and ΔCL ave = 0.74 at h/c = 0.055
Summary
For the effective utilization of wind energy, various research and development activities such as floating offshore wind power generation using largescale wind turbines and wind environment assessment. Yan et al [9] showed that there is a clear difference in the performance of the VAWT with NACA0018 airfoils even between h/c = 0.04 and h/c = 0.05 of inward Gurney flaps As a simple way to obtain the same effect as the blade camber, Gurney flaps were attached to the trailing edge of blade with a symmetrical airfoil as shown in Figure 1, and the effect of the flap height and direction, which relate to the degree and direction of camber, and the effect of the blade pitch angle on the performance of the small-scale VAWT were investigated. The degree of the camber effect can be changed by changing the flap height
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