Post-Stall Wind Tunnel Data for NACA 44XX Series Airfoil Sections: A Subcontract Report

Wind-turbine blades operate over a wide angle of attack range. Unlike aircraft, a wind turbine's angle of attack range extends deep into stall where the three-dimensional performance characteristics of airfoils are not generally known. Peak power predictions upon which wind turbine components are sized depend on a good understanding of a blade's post-stall characteristics. This report documentsresults of the wind tunnel investigation of constant chord nonrotating blades having four aspect ratios, with NACA 44XX series airfoil sections, at angles of attack ranging from -10 degrees to 110 degrees. Tests were conducted at Reynolds numbers ranging from 0.25 x 106 to 1.0 x 106. The thickness ratios studied were 0.18, 0.15, 0.12, and 0.09 . The aspect ratios were 6, 9 , 12, and infinity.Results of force and pitching moment measurements over the angle of attack range, for all combinations of Reynolds number, thickness, and aspect ratios, and the effects of boundary layer tripping are presented.