Convective enhancement on airfoils due to ice roughness elements in stagnation region flows.

Aircraft icing is a dangerous phenomenon which has been studied in-depth by researchers since the earliest days of aviation in order to improve safety for passengers and crew of aircraft operating in icing conditions. NASA's Icing Branch is a leading institution in this area. One of their most widely used tools is an icing prediction code known as LEWICE. Within LEWICE, the modeling of ice roughness and its effects on convective heat transfer can be improved to increase airframe and engine manufacturer confidence in LEWICE predictions. Building on several previous studies, this study examines the convective enhancement on airfoils in icing conditions due to ice roughness elements in stagnation region flows. Using the Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research Center, a test plate representing the leading 2% chord of a NACA 0012 was subject to various flow conditions. Three roughness patterns were utilized: a control surface representing an airfoil with no ice accretions, and two ice roughness surfaces geometrically scaled to match Reynolds numbers of a real ice shape generated in the Icing Research Tunnel (IRT). Roughness elements were modeled using both ABS plastic and aluminum in the scaled patterns. Temperature data from tests run in the VIST were used to calculate area averaged heat transfer coefficient values. The values from the roughness surfaces were compared to the control surface, showing convective enhancement as high as 400% in some cases. The data gathered during this study will ultimately be used to improve LEWICE or other ice accretion codes and create more accurate predictions of in-flight ice accretion on aircraft surfaces without the need for full-scale testing.