The wind is an energy source that has the properties of a clean, free, and readily available energy source. However, the efficiency of the existing rotors used to harness wind power is still not satisfactory. Thus, in this current study, the development and aerodynamic performance investigation of ten NACA airfoils comprising of five symmetrical and five non-symmetrical airfoils have been analyzed through the computational fluids dynamic (CFD) simulation approach. The main motive of this study was to investigate the aerodynamic performance of NACA airfoils to be used on a vertical axis wind turbine (VAWT), which will assist in further understanding the physics of the interaction between airflow and the wind turbine blades. The simulation was performed using two-dimensional computational models based on an unsteady state K-omega Shear Stress Transport (SST) turbulence model. This study covers a parametric study based on the variations of tip-speed ratios and constant wind velocity. The aerodynamic performances are evaluated in terms of torque, torque coefficient, and also power coefficient. The performance of NACA0018 was found to be the best among the other airfoils with a power coefficient of 0.3. NACA0010 displayed the lowest power coefficient among the other airfoils but had a more extensive operating range compared to the other airfoils. However, for non-symmetrical NACA airfoils, NACA2421 scored the highest power coefficient, followed by NACA4412. It was also found that most of the non-symmetrical NACA airfoils can operate at a higher range of tip-speed ratios compared to the symmetrical NACA airfoils.
Wind energy is known as renewable energy with the properties of the free, abundant and readily available source of energy. Wind power has now been seen as an alternative way to generate electricity. However, the existing wind turbines to harness this energy, which is used to transform wind kinetic energy into electricity still suffer low conversion capabilities. This study is therefore set out to evaluate the performance of a double-stage Savonius-type rotor while aiming to examine the effectiveness of this technique in increasing the efficiency while overcoming the inherent low inefficiency of the Savonius rotor. The simulations involved the use of the K-omega SST as the turbulent viscosity model. Three simulation models based on a different number of blades on the double-stage model are tested in terms of torque, power, torque coefficient and power coefficient. It is concluded that the double-stage technique was capable of enhancing the performance of the Savonius rotor. It was observed that more blades on a double-stage rotor have a negative effect on the performance of the Savonius rotor in terms of both torque efficiency and power efficiency. Comparing the three models, it was found that the two-blade model of the double-stage produced more torque and power output compared to the other three-blade and four-blade models of the double-stage Savonius rotor. Furthermore, the highest conversion efficiency in terms of power among all models occurs at the TSR of 0.6 with a corresponding maximum power coefficient of 18.4%.
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