Small Wind Turbine Blade Optimization using Blade Elementary Method Theory (BEMT)

Theoretical algorithms, such as computational fluid dynamics (CFD), blade elementary method (BEM) theory, and the vortex wake system (VWS) have been implemented in the design of aerodynamic wind turbines. On these theoretical methods, the (BEM) theory proved to be the best method in optimising HAWT blades and is thus the most commonly used approach in modelling and constructing small wind turbine blades. This paper will primarily focused on designing and optimizing the type of aerofoil required for improving the pitch angle of the rotor blades, and for determining the number of blades necessary to optimise the power output at various wind speed using BEMT. A NACA-4412 type aerofoil was chosen as the departure point for the blade design. Various pitch angles of 6°, 10° and 12° were chosen at an optimum angle of attack of 5°, 7° and 9°. A blade radius of 0.8- 1.0 m and chord length of 0.08-0.1 m were subsequently chosen for Designs 1, 2 and 3 respectively at various low wind speeds. At average wind speed of 0 - 2.3 m/s (8.28 km/h), 3-blade, 5-blade and 7-blade sets were designed and optimized for performance. During the design of the wind turbine blades, it was predicted that at various wind speeds, the rated output would be 7.5 W, 20 W and 40 W respectively Design 1, 2 and 3. The results for Design 1, with a blade radius of 0.85 m, a chord length of 0.06 m near the rotor hub, with a pitch angle of 6° at the rotor hub and a tapering off to about 1° at the blade radius tip of the blade, produced a maximum output power of 8.2 W at 4.2 km/h wind speed, and Design 2, with a blade radius of 0.95 m, a chord length of 0.08m near the rotor hub, with a pitch angle of 10° near the rotor hub and a tapering off to 1° at the blade radius tip of the blade, yielded a maximum output power of 12,5 W at 4.2 km/h wind speed and lastly Design 3, with a blade radius of 1m, a chord length of 0.1m near the rotor hub, with a pitch angle of 12° near the rotor hub and tapering off to 2° at the blade radius tip of the blade, generated a very useful power output of 39.5 W during testing. The maximum power output was achieved at an average wind speed of 1.17 m/s (4.2 km/h)