An Experimental Investigation on the Dynamic Ice Accretion and Heat Transfer Characteristics Over an Airfoil Surface Under Mixed-Phase Icing Conditions

Supercooled droplet icing and ice crystal icing are significant dangers to the safe operation of passenger aircraft and have been the focus of extensive experimental studies. Supercooled droplets and ice crystals may coexist in certain atmospheric regimes to create mixed-phase icing conditions, for which a significant scope for novel experimental investigations still remains. In the present study, a closed-loop icing wind tunnel with atomizing water spray nozzles and an ice crystal injection system is used to simulate mixed phase conditions. A NACA 0012 airfoil model with a 0.5 mm thick aluminum skin and 30% x/c electrothermal surface heating is instrumented with surface mounted thermocouples and heat flux sensors. High speed imaging is used to characterize ice formation. Six experiments are conducted at a freestream temperature of -10.0 ⁰C and velocity 40 m/s, the first four of which vary the initial leading edge temperature between an unheated condition and 5.0 ⁰C with a constant liquid water fraction of 0.4, while the subsequent two hold the leading edge temperature constant at 0.0 ⁰C and vary the liquid water fraction between 0.25 and 0.75. Unheated icing shows large leading edge ice growth and interaction between the release and absorption of latent heat due to freezing and melting. Higher initial temperatures show less ice growth and near net zero leading edge heat flux due to the presence of a thermally unsteady interfacial layer, with full ice shedding at an initial leading edge temperature of 5.0 ⁰C. A lower liquid water fraction at an initial leading edge temperature at 0.0 ⁰C shows thinner ice and more runback with melt dominated heat transfer, while a higher liquid water fraction shows more ice accretion, less runback, and freeze-dominated heat transfer behavior.