Abstract
Exploiting wind energy, which is a complex process in urban areas, requires turbines suitable for unfavorable weather conditions, in order to trap the wind from different directions; Savonius turbines are suitable for these conditions. In this paper, the effect of overlap ratios and the position of blades on a vertical axis wind turbine is comprehensively investigated and analyzed. For this purpose, two positive and negative overlap situations are first defined along the X-axis and examined at the different tip speed ratios of the blade, while maintaining the size of the external diameter of the rotor, to find the optimum point; then, the same procedure is done along the Y-axis. The finite volume method is used to solve the computational fluid dynamics. Two-dimensional numerical simulations are performed using URANS equations and the sliding mesh method. The turbulence model employed is a realizable K-ε model. According to the values of the dynamic torque and power coefficient, while investigating horizontal and vertical overlaps along the X- and Y-axis, the blades with overlap ratios of HOLR = +0.15 and VOLR = +0.1 show better performances when compared to other corresponding overlaps. Accordingly, the average Cm and Cp improvements are 16% and 7.5%, respectively, compared to the base with a zero overlap ratio.
Highlights
The increasing need for energy and the reduction of fossil fuel resources on one hand, and the strict laws on the environment and global warming on the other hand, draw governments’ attention to renewable energy resources [1,2,3]
The results showed that (1) the highest power coefficient of 0.00464 occurs from the wake of a bus on the passing lane, (2) the maximum power coefficient of two opposite moving cars on the passing lane is a little (7.5%) higher than the power coefficient of one car on the passing lane, (3) the rotor exerts negligible influences on the forces of the vehicles, and
The overlap ratio in different papers is sometimes defined slightly differently, but, in general, it expresses a common concept that Roy and Saha described in their article as the relation (1) [33]: Overlap Ratio = e/d where d is the chord of the blade and e is the overlap distance between the two blades (Figure 2)
Summary
The increasing need for energy and the reduction of fossil fuel resources on one hand, and the strict laws on the environment and global warming on the other hand, draw governments’ attention to renewable energy resources [1,2,3]. Roy and Saha [22] performed two-dimensional simulations using the k-ε model under the influence of the wall function and the SIMPLE algorithm in order to investigate the overlap ratios in conventional Savonius wind turbines. They acknowledged that these turbines would have a better efficiency at the overlap ratio of 0.2. Alom et al [32] performed two-dimensional simulations using the SST k-ω model in order to investigate the overlap ratios in an elliptical-bladed Savonius wind turbine. At the optimum point, the overlaps are checked along the Y-axis to eventually reach an optimal point
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