Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form rime ice or runback along the wing to form glaze ice. Most models so far have ignored the accretion of mixed ice, which is a combination of rime and glaze, possibly with entrapped air. The introduction of a parameter we term the "freezing fraction", defined as the fraction of a supercooled droplet that freezes on impact with top surface of the accretion ice, allows us to explore the concept of mixed ice accretion. Along with the freezing fraction, we consider different "packing densities" of rime ice, mimicking the different bulk rime densities seen in nature. Thus we consider ice accretion in four stages: rime, primary mixed, secondary mixed and glaze ice. Results match with existing models in limiting rime and glaze cases, but this mixed ice formulation provides additional insight into the composition of the overall ice structure, which ultimately determines adhesion and height. Freezing fraction increases with decrease in atmospheric temperature, with lower freezing fraction promoting glaze ice accretion. Future work entails parameterizing freezing fraction and packing density to include the effects of droplet size, wing curvature etc.
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