Abstract
To properly conduct a micro-siting of an orthopter-type vertical axis wind turbine (O-VAWT) in the built environment, this study investigated the effects of horizontal shear flow on the power performance characteristics of an O-VAWT by performing wind tunnel experiments and computational fluid dynamics (CFD) simulations. A uniform flow and two types of shear flow (advancing side faster shear flow (ASF-SF) and retreating side faster shear flow (RSF-SF)) were employed as the approaching flow to the O-VAWT. The ASF-SF had a higher velocity on the advancing side of the rotor. The RSF-SF had a higher velocity on the retreating side of the rotor. For each type of shear flow, three shear strengths (Γ = 0.28, 0.40 and 0.51) were set. In the ASF-SF cases, the power coefficients (Cp) were significantly higher than the uniform flow case at all tip speed ratios (λ) and increased with Γ. In the RSF-SF cases, CP increased with Γ. However, when Γ = 0.28, the CP was lower than the uniform flow case at all λ. When Γ = 0.51, the CP was higher than the uniform flow case except at low λ; however, it was lower than the ASF-SF case with Γ = 0.28. The causes of the features of CP were discussed through the analysis of the variation of blade torque coefficient, its rotor-revolution component and its blade-rotation component with azimuthal angle by using the CFD results for flow fields (i.e., horizontal velocity vectors, pressure and vorticity). These results indicate that a location where ASF-SFs with high Γ values dominantly occur is ideal for installing the O-VAWT.
Highlights
Since the 2000s, interest in installing small wind turbines (SWTs) in the built environment has been growing [1,2,3,4,5,6,7,8,9]
The results of the wind tunnel experiments and the computational fluid dynamics (CFD) simulations for the power performance of the orthopter-type vertical axis wind turbine (O-vertical-axis wind turbines (VAWTs)), such as the dependency of the power and torque coefficients on the tip speed ratio, the variations of the torque coefficients with azimuthal angle, are presented for the uniform flow case and the shear flow cases
The causes of the features of the power performance of the O-VAWT are discussed based on the CFD results of the flow fields
Summary
Since the 2000s, interest in installing small wind turbines (SWTs) in the built environment has been growing [1,2,3,4,5,6,7,8,9]. In the built environment, keeping the rotational speed of an SWT’s rotor as low as possible is preferable from the viewpoint of aerodynamic noise [10,11]. The optimal tip-speed ratio of an SWT in the built environment should be as low as possible, while the maximum power coefficient of the SWT should be as high as possible. In the built environment, VAWTs are preferable to HAWTs because VAWTs do not suffer, as much as HAWTs, from reduced energy outputs from frequent wind direction changes [12].
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