Bragg, M.B., Kerho, M.F. and Cummings, M.J., "Airfoil Boundary Layer Due to Large Leading-Edge Roughness", Paper No. 95-0536, AIAA 33rd Aerospace Sciences Meeting, Reno, NV, January 9-12, 1995.

Abstract

Hot-wire boundary-layer measurements were taken on a NACA 0012 airfoil with large leading-edge isolated and distributed roughness. The roughness was sized and located to simulate that seen on airfoils during the initial stages of glaze ice accretion. Velocity, turbulence intensity and turbulent intermittency data were acquired in the boundary layer for a variety of distributed roughness cases at low Mach number and Reynolds numbers from 0.75x106 to 2.25x106. The boundary-layer transition process began near the roughness elements, but fully developed turbulent profiles were not measured until approximately the airfoil 40% chord location. The roughness induced transition process was much less energetic, and developed much more slowly, than that observed on the model without roughness. For the model with isolated roughness on the leading edge, large critical roughness Reynolds numbers were found for the onset of boundary-layer transition. When the tunnel freestream turbulence was artificially raised to 0.95%, no laminar flow was observed on the model, only transitional and turbulent flow. In this case, the addition of leading-edge roughness had less affect on the boundary layer.