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The applicability of FENSAP-ICE-Unsteady to solve ice accretion on rotating helicopter blades is investigated using a two-bladed rotor and a generic cylinder, to represent a fuselage, for a forward flight test case. The unsteady rime ice accretion is simulated by coupling, at each time step, flow and water drop equations to the Messinger icing model. Mesh displacement effects are taken into account by an Arbitrary Lagrangian-Eulerian method. This new icing model is applied to rotor/fuselage flows by considering two grid domains: the first being fixed around the fuselage, and the second rotating with the blades. The gap region is stitched with tetrahedral elements to fully guarantee flow conservation.

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.

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.

CFD-Icing (CFD-I) is a powerful companion to CFD-Aero (CFD-A) in the design and certification of new aircraft, rotorcraft and jet engines. It can drastically reduce the number of tunnel and flight tests, and their associated costs, by simulating on computers the full Appendix C and beyond such as is proposed in new Appendices D and O. It can also predict performance and moment coefficients in roll, pitch and yaw. These predictions can then be used in original certification or supplemental certifications to the type design, allowing mitigating potential hazards of flight-testing. This work presents an example of the application of FENSAP-ICE to predict 45 minutes of ice accretion on a RC-26B aircraft fuselage retrofitted by the addition of a FLIR sensor and a SATCOM antenna. The predicted aerodynamic penalties are compared with recorded flight test data obtained with simulated ice shapes.