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The assessment of an unsteady approach for the simulation of in-flight electro-thermal de-icing using a Conjugate Heat Transfer (CHT) technique is presented for a NACA0012 wing and a swept wing. This approach is implemented in the FENSAP-ICE in-flight icing system, and provides simulation capabilities for the heat transfer and ice accretion phenomena occurring during in-flight de-icing with power cycling through several heater pads. At each time step, a thermodynamic balance is established between the water film, the ice layer and the solid domains. The ice shape is then modified according to ice accretion and melting rates. Numerical results show the complex interactions between the water film, the ice layer and the heating system. The NACA0012 validation test case compares well against one of the very few experimental de-icing test cases available in the open literature.

A CFD simulation methodology for the inclusion of the post-impact trajectories of splashing/bouncing Supercooled Large Droplets (SLDs) and film detachment is introduced and validated. Several scenarios are tested to demonstrate how different parameters affect the simulations. Including re-injecting droplet flows due to splashing/bouncing and film detachment has a significant effect on the accuracy of the validations shown in the article. Validation results demonstrate very good agreement with the experimental data. This approach is then applied to a full-scale twin-engine turboprop to compute water impingement on the wings and the empennage.

Two main approaches are available when studying droplet dynamics for in-flight icing simulations: the Lagrangian approach, in which each droplet trajectory is integrated until it impacts the vehicle under study or when it leaves it behind without impact, and the Eulerian approach, where the droplet dynamics is solved as a continuum. In both cases, the same momentum equations are solved. Each approach has its advantages. In 2D, the Lagrangian approach is easy to code and it is very efficient, particularly when used in combination with a panel method flow solver. However, it is a far less practical approach for 3D simulations, particularly on complex geometries, as it is not an easy task to accurately determine the droplet seeding region without a great number of droplet trajectories, dramatically increasing the computing cost. Converting the impact locations into a water collection distribution is also a complex task, since droplet trajectories in 3D can follow convoluted paths.

A CFD simulation methodology is presented to calculate blockage due to ice crystal icing of the IGV passages of a gas turbine engine. The computational domain consists of six components and includes the nacelle, the full bypass and the air induction section up to the second stage of the low-pressure compressor. The model is of a geared turbofan with a fan that rotates at 4,100 rpm and a low-pressure stage that rotates at 8,000 rpm. The flight conditions are based on a cruising speed of Mach 0.67 in Appendix-D icing conditions with an ice crystal content is 4.24 g/m3. Crystal bouncing, and re-entrainment is considered in the calculations, along with variable relative humidity and crystal melting due to warmer temperatures within the engine core. Total time of icing is set to 20 seconds. The CFD airflow and ice crystal simulations are performed on the full 6-stage domain. The initial icing calculation determines which stage will be chosen for a more comprehensive analysis.

The importance of the variation of relative humidity across turbomachinery engine components for in-flight icing is shown by numerical analysis. A species transport equation for vapor has been added to the existing CFD methodology for the simulation of ice growth and water flow on engine components that are subject to ice crystal icing. This entire system couples several partial differential equations that consider heat and mass transfer between droplets, crystals and air, adding the cooling of the air due to particle evaporation to the icing simulation, increasing the accuracy of the evaporative heat fluxes on wetted walls. Three validation cases are presented for the new methodology: the first one compares with the numerical results of droplets traveling inside an icing tunnel with an existing evaporation model proposed by the National Research Council of Canada (NRC).