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Abstract
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The Darrieus wind turbine has a low starting torque, which is one of its main disadvantages. The main objective of the present study is to design an advanced Darrieus wind turbine capable of self-starting at low wind speeds without extra components. This will allow us to utilize this sort of wind turbine in less windy regions, such as urban areas. The new design relied solely on the blade profile for exploiting the drag force caused by the wind on the blades. The profile modifications under consideration included a variety of cavity shapes, numbers, sizes, and positions on the blade surface. The Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations were numerically solved in combination with the SST k-ω turbulence model. The characteristics of power and torque, as well as their flow fields, were studied. The results demonstrated that the maximum enhancements of power and torque coefficients were achieved using a single cavity located on the upper surface of the trailing edge of the airfoil, namely UST airfoil. A maximum improvement of 18% for power coefficient was obtained using a UST airfoil with a Tip Speed Ratio (TSR) of 3.5. The UST airfoil has a circular shape with a diameter equal to 0.08 of airfoil chord length. The airfoil with a single cavity performed noticeably better than the airfoil with a dual cavity. However, the ULST airfoil which consisted of two cavities located on upper and lower surfaces of the airfoil trailing edge generated the maximum power coefficient among other airfoils. The ULST airfoil generated a CP value of 0.27 at TSR =3.5, representing a maximum improvement of 17% over an airfoil without a cavity.
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