A PDE-based 3D approach to in-flight ice accretion

Each year, sudden aircraft performance degradation due to ice accretion causes several incidents and accidents. Icing is a serious and not yet totally mastered meteorological hazard due to supercooled water droplets (liquid water droplets at a temperature below the dew point) that impact on aerodynamic surfaces. Icing results in performance degradations including substantial reduction of engine performance and stability, reduction in maximum lift and stall angle and an increase of drag. A realistic ice accretion simulation is achieved if the three contributing factors: the aerodynamic flow field, the water droplet trajectories, and the thermodynamic ice accretion process, are accurately modeled. A new approach to in-flight icing analysis is formulated and validated into this work. The methodology presented in this thesis is intended to be based on modern CFD algorithms to develop a useable new ice accretion tool for aircraft and engines, including: the solution of the 3D compressible turbulent Navier-Stokes equations; the computation of the collection efficiency by an Eulerian method; and a new module for the three-dimensional ice accretion process. To successfully complete the work, an appropriate turbulence model has been added to the existing flow solver. Therefore a part of this work has been the implementation and validation of the Spalart-Allmaras model. This turbulence model appeared to be robust and easy to use even in situation of complex 3D flow patterns encountered in icing. The new ice accretion model is expressed with mass and heat transfer balance at the aerodynamic surface using partial differential equations and four compatibility relations to close the system. An appropriate numerical scheme based on finite volume method is derived to solve the resulting system. 2D and 3D validations of the complete in-flight system (dry air flow field/droplets/ice accretion) conclude this work