الفهرس 
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Abstract
Vertical Axis Wind Turbines (VAWTs), which are one of the most promising wind energy harvesters have started recently to attract more and more attention due to their several advantages, especially in the small-scale wind turbines market. This study employed ANSYS Fluent software to numerically investigate the geometrical and operational parameters influencing the aerodynamic performance of VAWTs, such as the number of blades, blade thickness, blade camber, blade mounting position, blade pitch angle and turbine solidity. The four equations transition SST turbulence model has been employed to investigate the aerodynamic performance of several turbine models. The results obtained showed that increasing the number of blades from 2 to 4 blades increased the turbine time-veraged torque coefficient, 𝐶𝐶𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎, by 33.4%, while the maximum power coefficient, 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚, decreased by 7.0%. The present study also focused on investigating the blade thickness of symmetric airfoils of 12%, 15% and 18% of the chord length, the outcome of this investigation is that increasing the blade thickness from 12% to 18% of the chord length decreased both 𝐶𝐶𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎 and 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚 by 18.6%. Also, the effect of employing of symmetric and non-symmetric is investigated and the results of the study showed that the employment of non-symmetric airfoil (NACA 4412) instead of the symmetric airfoil (NACA 0012) dropped down the 𝐶𝐶𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎 and 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚 by 25.4%. Blade mounting position also analyzed through the present study, the results explained that mounting the blades at the centroid of the airfoil shape (42% of the chord length, measured from the leading edge in the chordwise direction) is the most proper position. Investigations of blade pitch angle adjustment also took place through the present study by analyzing three different Pitch angles, -1°, 0°, and +1°, the finding of this analysis is that the 0° pitch angle adjustment showed the best results in terms of 𝐶𝐶𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎 and 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚, while the +1° pitch angle adjustment decreased both 𝐶𝐶𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎 and 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚 by 26.3%. On the other hand, a number of CFD simulations are carried out for different turbine solidities of 0.18, 0.24, 0.30 and 0.36 by changing the chord length to figure the relation between the turbine solidity and performance, the outcome of the investigation is that increasing the solidity from 0.18 to 0.36 boosted 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚 by 23.2%. The study also investigated the effect of slotted airfoils on VAWTs, the simulations confirmed that the resulted power coefficient could achieve 36.3% by adding a slot to the airfoil. Finally, by adding Trailing-Edge Flap (TEF) improved the 𝐶𝐶𝑃𝑃𝑚𝑚𝑎𝑎𝑚𝑚 by almost 30% increase compared to the base model to reach more .