A Three-Layer Model for Ice Crystal Icing in Aircraft Engines

This paper presents the current state of a three-layer surface icing model for ice crystal icing risk assessment in aircraft engines, being developed jointly by Ansys and Honeywell to account for possible heat transfer from inside an engine into the flow path where ice accretion occurs. The bottom layer of the proposed model represents a thin metal sheet as a substrate surface to conductively transfer heat from an engine-internal reservoir to the ice layer. The middle layer is accretion ice with a porous structure able to hold a certain amount of liquid water. A shallow water film layer on the top receives impinged ice crystals. A mass and energy balance calculation for the film determines ice accretion rate. Water wicking and recovery is introduced to transfer liquid water between film layer and porous ice accretion layer. Numerical tests have been conducted to verify new model behaviors like substrate surface heat absorption into the accretion layer in the form of meltwater, water recovery into the film, water saturation of the accretion layer with adhesion loss and shedding risk. The proposed model, along with a new compound sticking and erosion model, is validated against selected cases from NRC’s wedge icing tests. The bouncing and erosion effect is proven crucial in the modeling. In the end, simulation of ice crystal icing within a turbofan engine at high altitude is presented. Ice crystal cloud thermodynamics have been analyzed and correlation is explained among key crystal variables like wet-bulb temperature and melt ratio. Finally, the limitations of this model are clarified.