Abstract
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 (ks/ds) 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 > ks/ds > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (Cp) occurred under the condition of TSR = 4, α = 5%, ks/ds = 1 × 10−2, and TI = 8%.
Highlights
Wind turbines can be categorized into horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) [1,2]
The instantaneous power coefficient of the blades returns to normal after they pass through the region that influenced by the shaft wake
When the VAWT operates to the revolution, the frequency of the shedding vortices is substantially different from that of the current revolution
Summary
Wind turbines can be categorized into horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) [1,2]. The HAWTs have been extensively employed in the large scale wind farm far away from urban areas due to the loading noise that is created by the large rotors [3,4]. In order to increase the power of the HAWTs, the size of the turbine is getting larger than before and this brings difficulties to the maintenance of the wind farm [5]. In contrast to HAWTs, VAWTs have less commercial applications; the power generation capacity of VAWTs is less than that of HAWTs [6,7,8]. VAWTs have some noteworthy advantages, for instance, the VAWTs can capture unstable and turbulent wind energy from any direction, and they produce less noise. The VAWTs are Energies 2018, 11, 1870; doi:10.3390/en11071870 www.mdpi.com/journal/energies
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