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In order to ensure flight safety in icing conditions and meet FAA or other national aircraft certification regulations, which require an aircraft to be able to safely operate throughout the icing envelope of Part 25 Appendix C, ice protection mechanisms have to be employed on critical locations of an aircraft. Among different anti-icing mechanisms, hot bleed air systems are the most reliable and efficient ones, and are widely used on commercial aircraft to protect critical surfaces such as leading edge wing panels and high lift devices, empennage surfaces and engine nacelle lip. Due to the complexity of anti-icing experiments and flight tests, advanced numerical simulation of complex thermal anti-icing systems has been highly anticipated as a supplementary design and certification tool. CHT3D [1], the new 3-D Conjugate Heat transfer module of FENSAP-ICE [2] for the simulation of hot air and electrothermal ice protection, will be presented in this paper.

Numerically predicted roughness distributions obtained in in-flight icing simulations with a beading model are used in a quasi-steady manner to compute ice shapes. This approach, called "Multishot," uses a number of steady flow and droplet solutions for computing short intervals (shots) of the total ice accretion time. The iced geometry, the grid, and the surface roughness distribution are updated after each shot, producing a better match with the unsteady ice accretion phenomena. Comparisons to multishot results with uniform roughness show that the evolution of the surface roughness distribution has a strong influence on the final ice shape. The ice horns that form are longer and thinner compared to constant roughness results. The constant roughness approach usually fails to capture the formation of the pressure side horns and under-predicts the thickness of the ice in this region.

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.