High-Speed Imaging to Quantify Transient Ice Accretion Process over an Airfoil

Ice accretion on aircraft wings poses a performance and safety threat as aircraft encounter supercooled droplets suspended in the cloud layer. The details of the ice accretion depend on the atmospheric conditions and the flight parameters. The icing process on the wing consists of a complex interaction of water deposition, surface water transport, and freezing. The aerodynamics affect the water deposition, the heat and mass transport, and ice accumulation; meanwhile, the accumulating ice affects the aerodynamics. Until now, most experimental measurements of aircraft icing have focused on the final ice shapes formed after exposure for a set duration to icing conditions. This approach fails to capture the transient processes that form the final ice formations. Here, we present experiments conducted in the Iowa State Icing Research Tunnel on a NACA 0012 airfoil to study the transient ice accretion process under varying icing conditions. High-speed video of the icing process was acquired under controlled environmental conditions to quantitatively measure the transient water film runback, rivulet formation, and accumulated ice growth. Image processing techniques were developed to extract physical information from the acquired image sequences of the icing events. The experiments demonstrate how varying the environmental conditions modifies the ice accretion process. It was found that the leading-edge ice growth rate is proportional to water deposition rate and the rivulet spacing and rivulet area coverage decrease with increasing wind speed. The water rivulet runback speed over the airfoil surface was found to increase rapidly with increasing wind speed.