Two-Dimensional Subsonic Wind Tunnel Tests of Two 15-Percent Thick Circulation Control Airfoils
Abstract
Two relatively thin Circulation Control (CC) elliptic airfoils were tested subsonically to determine their characteristics as proposed helicopter rotor tip sections. These airfoils, employing tangential trailing edge (Coanda) blowing, had shown very promising transonic characteristics in previous tests. It was the purpose of the subonic retests to determine if these thin sections could generate low speed characteristics which would be equally impressive. Due to its more forward slot location, the 15-percent thick pure elliptic section displayed effective subsonic operation at positive angle of attack, reducing drag while producing lift coefficients up to 3.5. The rounded trailing edge configuration, with further aft slot and better Coanda deflection of the jet, generated lift coefficients up to 4.25 (with a preference for negative incidence), but experienced higher drag levels. As a result of the small nose radii and low test Reynolds number, both sections were limited in performance by leading edge separation. At a fixed momentum coefficient, variation in slot height indicated that better performance was obtained for reduced heights. This was due primarily to higher energy levels in the jet sheet, but the lower bound on slot height was limited by boundary layer building in very small nozzles. Comparison of both CC sections to the more conventional NACA 0012 blade section indicated far greater lift capabilities with circulation control. However, due to blowing power requirements, equivalent efficiency was less at positive incidence, than for the conventional section.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1971
- Accession Number
- AD0900210
Entities
People
- David W Taylor
- Robert J. Englar