Abstract
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 as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of rime and glaze. A parameter we term the “freezing fraction” is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different “packing densities” of rime ice, mimicking the different bulk rime densities observed in nature. Ice accretion is considered in four stages: rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and experimental data in the limiting rime and glaze cases. The mixed ice formulation however provides additional insight into the composition of the overall ice structure, which ultimately influences adhesion and ice thickness, and shows that for similar atmospheric parameter ranges, this simple mixed ice description leads to very different accretion rates. A simple one-dimensional energy balance was solved to show how this freezing fraction parameter increases with decrease in atmospheric temperature, with lower freezing fraction promoting glaze ice accretion.
Highlights
Ice accretion is a natural phenomenon that affects a wide range of external engineering structures, such as aircraft, power cables, radio masts and wind turbines
The mixed ice formulation provides additional insight into the composition of the overall ice structure, which influences adhesion and ice thickness; and shows that for similar atmospheric parameter ranges, Preprint submitted to Physics of Fluids this simple mixed ice description leads to very different accretion rates
This paper considers the formation of mixed ice on an aircraft wing from the partial freezing of impinging supercooled droplets, which deposit onto the growing interface as a combination of solid rime ice particles and water
Summary
Ice accretion is a natural phenomenon that affects a wide range of external engineering structures, such as aircraft, power cables, radio masts and wind turbines. This paper considers the formation of mixed ice on an aircraft wing from the partial freezing of impinging supercooled droplets, which deposit onto the growing interface as a combination of solid rime ice particles and water. We characterise this as a multiphase layer comprising a porous medium created by the solid rime ice particles and water at longer accretion times and different atmospheric conditions. (d) Once this mixed ice layer is again too thick to transport released latent heat on the droplets freezing, a water film forms on its surface This may be supplemented by runback water formed by melting ice formations at the wing leading edge. Formation of a porous ice matrix layer within this model enables more general possibilities to explore in the future, such as forced convective transfer modes
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