سيد يوسف سجادي

The increasing demand for clean energy sources as a substitute for fossil fuels has made the utilization of wind energy indispensable. Vertical axis wind turbines (VAWTs) offer a suit-able option for harnessing wind power in urban environments. VAWTs can be categorized into two main types: Darrieus and Savonius, which utilize lift and drag forces, respectively, to generate rotational motion. Darrieus turbines often face challenges in starting rotation at low rotational speeds. Savonius turbines, on the other hand, can initiate rotation at lower speeds compared to Darrieus turbines. Hybrid Darrieus-Savonius turbines have shown promise in addressing the self-starting issue. This thesis investigates and analyzes a hybrid Darrieus-Savonius VAWT, where a Savonius rotor is integrated into the inner structure of a Darrieus rotor. This hybrid design aims to enhance the overall performance and efficiency of wind turbines. Various hybrid turbine geometries were examined, varying the ratio of the Savonius rotor diameter to the Darrieus rotor diameter. The Darrieus rotor diameter was kept constant, while the Savonius rotor diameter was varied from 0.2 to 0.7 times the Dar-rieus diameter. To eva‎luate the performance of these geometries, unsteady computational fluid dynamics (CFD) simulations were conducted at tip speed ratios ranging from 0.9 to 2.3. Additionally, the influence of varying the airfoil thickness of the Darrieus blades on the power coefficient of the hybrid turbine was investigated. Consequently, unsteady CFD sim-ulations were performed for different Savonius-to-Darrieus diameter ratios using NACA0015, NACA0018, and NACA0021 airfoils for the Darrieus blades. The simulation results include the calculation of the generated torque coefficient, power coefficient, and maximum torque coefficient for each geometry and simulation condition. The final conclu-sion is that the NACA 0015 airfoil is better suited for strong winds and high TSRs, the NACA 0018 airfoil is more appropriate for high wind speeds and TSRs above 1.8, and the NACA 0021 airfoil is a better choice for mild winds and low TSRs. Additionally, a radial ratio of 0.6 for Savonius to Darrieus turbines has been identified as the optimal value for maximizing torque production, and this should be considered as a key factor in the design of wind turbines.

تحليل عددي , توربين باد عمود محور , جريان آشفته , عملكرد آيروديناميكي

numerical analysis , vertical axis wind turbine , turbulent flow , aerodynamic performance

Seyed Yousef Sajjadi

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