In-flight ice accretion can occur in two ways. It can happen when an aircraft flies through a cloud composed of supercooled droplets, or it can occur in the presence of ice crystals.
Supercooled droplet icing happens when an aircraft passes through a cloud in which the droplets are at a temperature below freezing, but they remain in a liquid phase. Ice crystal icing, on the other hand, occurs when the aircraft encounters clouds where the water content has already fully or partly solidified, forming ice crystals.
The state of these droplets and crystals, whether they solidify into ice or melt into liquid water, is influenced by flight conditions and the temperature of the surface upon impact. Depending on the case, they may freeze instantly, forming a layer of ice, or they may initially form a thin liquid film which, over time, freezes and develops into a layer of ice.
This problem is interdisciplinary by nature. Both ice crystal icing and supercooled droplet icing result from the interplay of several elementary physical processes, and their modeling requires the use of various sciences: meteorology, material science, aerodynamics, fluid mechanics, solid mechanics, thermodynamics flight physics, power management and control, etc.
Aircraft icing can lead to numerous detrimental effects such as reduction of visibility, damage due to ice shedding, blockage of probes and static vents, reduced flight performance, adverse aerodynamic effects, and engine power loss. These in-service events can, in turn, lead to major disruption of air operation and aircraft maintenance.
In EASA’s 2019 annual report, in-flight icing, encompassing both supercooled droplet and ice crystal icing, was identified as a priority 1 issue for large airplanes. Thus, to comply with certification rules, airframes and engine manufacturers must demonstrate safe operation under these icing conditions, which incurs significant costs before the new product is put into service.
Wind tunnel tests and flight tests in icing conditions are usually required due to the low confidence certification authorities place in simulations due to the complexity of the icing process. A breakthrough, leading to a reduction of time-to-market and certification costs, would be obtained by creating a consensus among certification authorities about the reliability of simulation tools for predicting in-flight ice accretion, including ice crystal icing, and the operation of IPS.
TRACES is a European Joint Doctorate network whose main goal is to provide high-level training in the field of in-flight icing to deliver a new generation of high achieving Doctoral Researchers (DR) in the disciplines necessary for comprehending the complexity of ice accretion, including ice crystal icing, and its mitigation in aircraft and aeroengines.
More information about our network: https://traces-project.eu/