The central shaft is an important and indispensable part of a small scale urban vertical axis wind turbines (VAWTs). Normally, it is often operated at the same angular velocity as the wind turbine. The shedding vortices released by the rotating shaft have a negative effect on the blades passing the wake of the wind shaft. The objective of this study is to explore the influence of the wake of rotating shaft on the performance of the VAWT under different operational and physical parameters. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 9%, the power loss of the wind turbine in one revolution increases from 0% to 25% relative to that of no-shaft wind turbine (this is a numerical experiment for which the shaft of the VAWT is removed in order to study the interactions between the shaft and blade). When the downstream blades pass through the wake of the shaft, the pressure gradient of the suction side and pressure side is changed, and an adverse effect is also exerted on the lift generation in the blades. In addition, α = 5% is a critical value for the rotating shaft wind turbine (the lift-drag ratio trend of the shaft changes differently). In order to figure out the impacts of four factors; namely, tip speed ratios (TSRs), α, turbulence intensity (TI), and the relative surface roughness value (k s /d s ) on the performance of a VAWT system, the Taguchi method is employed in this study. The influence strength order of these factors is featured by TSRs > k s /d s > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (C p ) occurred under the condition of TSR = 4, α = 5%, k s /d s = 1 × 10 −2 , and TI = 8%.

No abstract

The shaft is a very important part of small scale vertical axis wind turbines (VAWTs) being used in urban environments. The shedding vortices will be formed as wind passes around the shaft, the shedding vortices released by the shaft have a negative effect on the aerodynamic performance of the blades passing the wake of the wind shaft, and this will lead to lower power output of the wind turbine. The objective of this study is to explore the differences of the effect of the rotating and non-rotating shafts of VAWTs on the aerodynamic performance of small scale urban VAWTs. In addition, the effect of surface roughness on the performance of the rotating and non-rotating shaft wind turbines is also investigated. The dynamic analysis of the VAWT is carried out by the method of Computational Fluid Dynamics. The aerodynamic loads in the study are obtained by solving the two-dimensional (2D) unsteady Navier-Stokes equations with the Transition SST turbulence model. The results are validated with experimental results. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 3.9%, the power coefficient (Cp) of the rotating shaft wind turbine is 2.2% higher than that of the non-rotating shaft wind turbine. Increasing the shaft diameter-based Reynolds number (Res) will increase the Cp of rotating and non-rotating shaft wind turbines, when Res is 2.6 × 104 and the Cp of the non-rotating shaft wind turbine is 5.7% higher than that of the rotating shaft wind turbine. The Cp of the non-rotating and rotating shaft wind turbines is reduced by 6.9% and 6.3%, respectively, by increasing the turbulence intensity from 4% to 16%. The optimal power output occurs under the condition of the non-rotating shaft wind turbine, and the relative surface roughness (ks/ds) is 0.005, where it is observed that Cp increased by 2.1% in comparison to that of the smooth shaft wind turbine.