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Recent aircraft incidents and accidents have highlighted the existence of icing cloud characteristics beyond the actual certification envelope defined by the JAR/FAR Appendix C, which accounts for an icing envelope comprising water droplets up to a diameter of 50 μm. The main concern is the presence of SLD (Supercooled Large Droplets), with droplet diameters well beyond 50 microns. In a previous European-funded project, EURICE, in-flight icing conditions and theoretical studies were performed to demonstrate the existence of SLD and to help characterize SLD clouds. Within the EXTICE project the problem of SLD simulation is addressed with both numerical and experimental tools is being addressed. In this paper the objectives and main achievements of the EXTICE project will be described.

Two-dimensional models have been developed to predict and reproduce ice accretion shapes on airfoil profiles. These simulated shapes mostly are similar to experimental forms. However, in some conditions, the ice shapes could present some discontinuity along span showing some ice deposit separated by air inclusion: this deposit is called “lobster tail” or “scallop icing”. The classical 2D approaches fail to predict this kind of ice shapes. The 3D simulation requires to take into account a fully detailed heat and mass balance parameters which scallop accretion is sensitive. For that, the scallop formation was experimentally led on the swept cylinders. An experiment in the icing wind tunnel PAG of the CEPr (The French Engine Test Center) was conducted in order to characterize the phenomenon and find the most relevant criteria. The ice accretions were obtained at different conditions.