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Ice accretion is a purely unsteady phenomenon that is presently approximated by most icing codes using quasi-steady modeling. The accuracy of ice prediction is thus directly related to the prescribed time step, or the time span during which the impact of ice growth on both flow and droplets can be neglected. Such approximation is removed by FENSAP-ICE-Unsteady which fully couples in time a diphasic flow (interacting air and droplet particles) with ice accretion. The two-phase flow is solved using the Navier-Stokes and Eulerian droplet equations, while the water film characteristics and ice shape are obtained from the conservation of mass and energy within a thin film layer. The iced surface being constantly displaced in time, Arbitrary Lagrangian-Eulerian terms are added to the governing equations to account for mesh movement. For rime ice, numerical results show that full unsteady modeling improves the accuracy of ice prediction when compared to one-shot ice accretion.

A fully CFD-based methodology for ice particle tracking based on a Monte Carlo statistical approach and a six-degrees-of-freedom particle-tracking module has been developed within the FENSAP-ICE in-flight icing system. A one-way aerodynamic coupling between the airflow and the ice particle has been adopted, such that the flowfield determines the forces and moments on the particle at each location on its track, but the particle, being much smaller, has no aerodynamic effect on the aircraft's flowfield. A complete envelope of force and moment coefficients has been computed for a representative ice shape, in order to generate a permanent database. At each time step during the integration of the particle track, the angles of the local flow velocity vector with the principal axes of the particle are determined and used to interpolate the corresponding force and moment coefficients from the particle's database. These 6-DOFs are then used to compute the next particle location.