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Numerical in-flight icing simulations have become a powerful tool in the type-certification process of commercial aircraft, helping to focus and reduce the number of flights in natural icing conditions and icing wind tunnel tests. Despite the numerical software's sophistication, applicants should always validate it for various icing conditions, and show good predictability to the aviation authorities. Icing being a key certification issue for the design of such aircraft because of its direct link to flight safety, MHI (Mitsubishi Heavy Industries) has early on adopted FENSAP-ICE and integrated this 3-D icing software into its Regional Jet program. The objective of this paper is to validate, on geometries of significance to MHI, this numerical tool for accuracy in predicting the flow field, droplet impingement and ice shapes. This step is required prior to integrating the software in the actual design process.

The irregular shapes that glaze ice may grow into while accreting over the surface of an aircraft represent a major difficulty in the numerical simulation of long periods of in-flight icing. In the framework of Arbitrary Lagrangian-Eulerian (ALE) formulations, a mesh movement scheme is presented, in which frame and elasticity analogies are loosely coupled. The resulting deformed mesh preserves the quality of elements, especially in the near-wall region, where accurate prediction of heat flux and shear stresses are required. The proposed scheme handles mesh movement in a computationally efficient manner by localizing the mesh deformation. Numerical results of ice shapes and the corresponding aerodynamic coefficients are compared with the experimental results.

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.

FENSAP-ICE is a second generation CFD-based in-flight icing simulation system, bringing to the icing field simulation advances widely used by the aircraft and turbo machinery industries. It is built in a modular and interlinked fashion to successively solve each of flow, impingement, accretion, heat loads and performance degradation via field models based on the Euler/Navier-Stokes equations for the clean and degraded flow, and new partial differential equations for the other three icing processes. This paper presents the FENSAP-ICE system and shows examples of its use to calculate impingement and ice shapes on a 3D helicopter rotor blade tip and on a nacelle inlet.

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.

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.

The FENSAP-ICE system was first conceived for fixed-wing aircraft and air induction system icing, but major developments are underway to augment its capabilities for icing simulation of rotorcraft and tiltrotor aircraft. A project is underway, under the auspices of the RITA (Rotorcraft Industry Technology Association) to reduce icing certification flight tests through use of second-generation three-dimensional (3D) Computational Fluid Dynamics (CFD) based technologies. The plan is to supplement traditional icing tunnel and flight-testing with modern 3D inflight icing simulation tools that facilitate the development and certification of all-weather operations rotorcraft and tilt-rotor aircraft. A viscous fully 3D ice accretion and runback modeling capability is being developed and initial correlation studies to both 2D and 3D icing test cases have produced very good results.

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.

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.