Aerodynamic Evaluation of Gottingen and Joukowski Airfoils for Use in Rotors of Small Wind Turbines

Abstract

Climatic changes and global warming resulting from production and utilization of fossil fuels and other human activities accelerated research to replace effectively fossil fuels. Wind energy appears at the top of the list of the viable candidates to reduce dependence on fossil fuels. The technology for large and medium wind turbines is well dominated and usually installed to supply electricity for distribution grids. Small wind turbines are usually installed in remote and isolated areas. This work investigates alternative airfoils, Gottingen and Joukowski, for application in small wind turbines capable to operate efficiently at small wind velocities. The investigation includes aerodynamic analysis of the effects of varying airfoil, the chord distribution and number of blades on the torque and power coefficients. A home-built numerical code based on the Blade Element Momentum (BEM) theory validated against available experimental and numerical results is used. The numerical code and the Xfoil software were used to adjust the aerodynamic data of the airfoils. The elliptic chord distribution and the linearly tapered blades are found to be viable and efficient. The increase of the number of blades increases the torque at low velocities but not enough to achieve the maximum power. Friction losses and limitations imposed by the rotational speed due to high solidity ratios reduce the gains in efficiency of rotors with more than four blades. The airfoils J9.513 and GO447 are found more efficient than the reference airfoil S832 at small velocities but show inferior performance at speed ratios more than 7.