Design of a low Reynolds number airfoil for small horizontal axis wind turbines

Abstract

A low Reynolds number airfoil was designed for applications in small horizontal axis wind turbines to achieve better startup and low wind speed performances. Experiments were performed on the improved airfoil (AF300) in an open circuit wind tunnel at Reynolds numbers of 38,000, 75,000, 128,000 and 205,000. Pressure distributions were obtained over the surface of the airfoil and the lift and drag forces were measured with a dynamometer at different angles of attack, α. A CFD analysis was also performed to get additional information on the flow characteristics. Particle Image Velocimetry (PIV) together with smoke flow visualization were used to study the flow around the airfoil. At the Reynolds numbers of 75,000, 128,000 and 205,000, maximum lift coefficients of 1.72, 1.81 and 1.86 respectively were obtained at the stall angle of 14°. The lift coefficient increased from 0.41 to 1.05 at Re = 38,000 in the α range of 0–18°, in which no stalling was documented. The results from PIV and smoke flow visualization showed that the flow stayed fully attached to the airfoil surface from Re as low as 56,000 at an angle of attack of 8° and maintained a fully attached flow up to 14° angle of attack for Re as low as 75,000.

Keywords

• Horizontal axis wind turbine; 
• Airfoil; 
• Wind tunnel testing; 
• Particle image velocimetry;
• Adverse pressure gradient; 
• Flow characteristics
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