Aerodynamic Performance of Small Wind Turbines Operating at Low Reynolds Numbers

In an effort to enhance the aerodynamic performance of small horizontal axis wind turbines (HAWTs), an extensive design study was carried out with an airfoil database. Since small HAWTs operate at low Reynolds number along the entire span of the blades, the use of airfoils specially designed for this flow regime instead of the airfoils traditionally used should improve energy capture. Sinceairfoil performance at low Reynolds numbers is hard to predict, all of the airfoils considered in this study were tested in a wind tunnel in order to obtain accurate airfoil data. The blade shapes for a 5 kW/5 m diameter rotor operating at a nominal tip speed ratio of 10 were designed with the optimization code PROPGA. Results for design and off-design conditions are provided to show theimportance of having low drag over a broad range when it is not possible to hold the tip speed ration constant.