Vortex Shedding Noise of an Isolated Airfoil.
Final rept. 30 Jun 69-28 Dec 71,
UNITED AIRCRAFT RESEARCH LABS EAST HARTFORD CONN
Pagination or Media Count:
The purpose of the study was to determine the vortex shedding noise characteristics of isolated airfoils in a Reynolds number range applicable to full-scale helicopter rotors. Measurements of far-field noise, airfoil surface pressure fluctuations, and correlation coefficients were obtained for three airfoils. Two models of differing thickness were tested as two-dimensional models NACA 0012 and 0018 airfoils and the third has a span of half the tunnel width NACA 0012 airfoil. Airfoil vortex shedding noise was found to be discrete rather than broadband. The frequency dependence of this noise on velocity and chord was found to be well predicted by a constant Strouhal number near 0.2 referenced to laminar wake thickness at the airfoil trailing edge. The presence of a laminar boundary layer on the pressure surface of the airfoils was found to be critical to the presence of vortex shedding noise. Author