AERODYNAMIC DESIGN OF VERTICAL AXIS WIND TURBINES USING BLADE ELEMENT MOMENTUM THEORY AND WIND DATA IN THE PROVINCE OF SOUTH KHORASAN
Recent works in design of small stall regulated wind turbines has indicated the need to provide site-specific small wind turbines which incorporate innovative design and new materials of construction leading to better performance. In this paper, vertical axis wind turbines are considered for simplicity and ease of manufacturing for limited applications in Iran. Blade element momentum (BEM) theory is employed for aerodynamic design and analysis of a vertical axis wind turbine. The design algorithm was programmed in MATLAB routines using an iterative method for calculating axial and swirl induction factors, u and u', respectively. NACA4415 aerofoil is used to provide higher lift to drag ratio and a double multiple stream tube model is used to properly model upstream and downstream of wind turbine in better agreement with some experimental observations. For the airfoil section NACA4415, the lift to drag ratio of 130 is obtained at the angle of attack of 13 degrees. A parabolic fitting function for lift and a cubic fitting function for drag coefficients are used with respect to angle of attack. This approach allows better predictions in high angle of attacks when partial stall may occur over airfoil surfaces. Studying wind energy potential in four stations, Bojnord, Esfaraein, Fadashk and Nehbandan in two provinces of North and South Khorasan in Iran, the results indicated that Fadashk station has better wind potential for setting up wind turbine in the studied provinces. The study was performed based on the annual wind speed data obtained from renewable organization (SUNA) in Iran. Statistical analysis based upon wind data in Fadashk in the province of south Khorasan is used for designing a 1.5 kW vertical axis (H-rotor) wind turbine. Our results for the wind turbine are verified with an existing wind turbine and are parametrically studied. Furthermore, economical aspects of installing wind turbines in Fadashk and re cup from wind energy are investigated. The economical feasibility of the designed VAWT is finally evaluated to predict annual production of electricity that shows 6 cent profit for each kW h generated power.