| Bragg, M.B., Cummings, M.J., Lee, S. and Henze, C.M., "Boundary-Layer and Heat-Transfer Measurements on and Airfoil with Simulated Ice Roughness", AIAA Paper No. 96-0866, Reno, NV, Jan. 15-18, 1996. |
| Hot-wire boundary-layer measurements were taken on a NACA 0012 airfoil with leading-edge hemispherical distributed roughness which was 0.35 and 0.75 mm high and spaced 1.3 diameters apart. 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. Convective heat transfer information was obtained from infrared imaging of the airfoil surface downstream of the distributed surface roughness. 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. At all but the smallest Reynolds number and roughness height, the convective heat transfer downstream of the roughness was increased as much as 2.5 times the laminar boundary layer value. The tunnel freestream turbulence was artificially raised to 0.50% and 0.95% to simulate the higher turbulence levels seen in icing wind tunnels. Increasing the tunnel turbulence level to 0.5% moved T-S boundary-layer transition forward for the low Re case. At 0.95% freestream turbulence and high Re, no laminar flow was observed on the model, only transitional and turbulent boundary-layer flow. In this case, the addition of leading-edge roughness had less affect on the boundary layer. |