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A series of turbofan engine malfunctions characterized by flameout and rollbacks at high altitudes have been reported and analyzed by flight safety agencies and concerned industries1. Conclusions pointed the source of these incidents to be an ice accretion build-up in the low-pressure compressor of the turbofan explained by the presence of ice crystals in the flying environment. In order to provide a numerical tool to analyze such situations, a new capability is developed within FENSAP-ICE2 that provides an unsteady model for ice crystals accretion in jet engines. The first step of this study is concentrated on adapting FENSAP-ICE to turbomachinery problems. A 3D unsteady parallel approach for rotor-stator interaction is developed, allowing the treatment of multi-stage blade motion in mixed relative and absolute frames of reference via a finite element interpolation method at interfaces3. The approach is demonstrated using the NASA compressor stage 35.

The high computational cost of 3-D viscous turbulent aero-icing simulations is one of the main limitations to address in order to more extensively use computational fluid dynamics to explore the wide variety of icing conditions to be tested before achieving aircraft airworthiness. In an attempt to overcome the computational burden of these simulations, a Reduced Order Modeling (ROM) approach, based on Proper Orthogonal Decomposition (POD) and Kriging interpolation techniques, is applied to the computation of the impingement pattern of supercooled large droplets (SLD) on aircraft. Relying on a suitable database of high fidelity full-order simulations, the ROM approach provides a lower-order approximation of the system in terms of a linear combination of appropriate functions. The accuracy of the resulting surrogate solution is successfully compared to experimental and CFD results for sample 2-D problems and then extended to a typical 3-D case.