Convection from a Simulated NACA 0012 Airfoil with Realistic Ice Accretion Roughness Variations

Changes in convection coefficient caused by the changes in surface roughness characteristics along an iced NACA 0012 airfoil were investigated in the 61-cm by 61-cm (24 in. by 24 in.) Baylor Subsonic Wind Tunnel using a 91.4-cm (36-in.) long heated aerodynamic test plate and infrared thermometry. A foam insert was constructed and installed on the wind tunnel ceiling to create flow acceleration along the test plate replicating the scaled flow acceleration the along the leading 17.1% (3.6 in.) of a 53.3-cm (21-in.) NACA 0012 airfoil. Two sets of rough surface panels were constructed for the study, and each surface used the same basic random droplet pattern created using the Lagrangian droplet simulator of Tecson and McClain (2013). For the first surface, the roughness pattern was replicated with the same geometry over the plate following a smooth-to-rough transition location noted in historical literature for the case being replicated. For the second surface, the heights of the roughness elements were scaled along the streamwise direction to match the roughness variations measured in the Icing Research Tunnel at NASA Glenn Research Center using laser scanning for an unswept 53.3-cm (21-in.) NACA 0012 airfoil exposed to a supercooled large droplet icing condition. The measured convective enhancements are comparable to historical measurements of convection from airfoils with simulated ice roughness.