Aerodynamic optimisation of a small-scale wind turbine blade for low windspeed conditions

Wind conditions in South Africa dictate the need for a small-scale wind turbine to produce usable power at windspeeds below 7m/s. In this project, a range of windspeeds, within which optimal performance of the wind turbine is expected, was selected. The optimal performance was assessed according to the Coefficient of Power (C-P), which rates the turbine blade's ability to extract energy from the available wind stream. The optimisation methods employed allowed a means of tackling the multi-variable problem such that the aerodynamic characteristics of the blade were ideal throughout the windspeed range. The design problem was broken down into a two-dimensional optimisation of the airfoils used at the radial stations, and a three-dimensional optimisation of the geometric features of the wind rotor. By means of blending various standard airfoil profiles, a new profile was created at each radial station. The combined panel method-boundary layer-wake code, XFOIL was used for the two-dimensional analysis of these airfoils. 3D optimisation involved representation of the rotor as a simplified model and use of the Blade Element Momentum (BEM) method for analysis. An existing turbine blade, from which the design specifications were moulded, was further used for comparative purposes throughout the project. The resulting blade design offers substantial improvements on the reference design. The application of optimisation methods has successfully aided the creation of a wind turbine blade with consistent peak performance over a range of design points.