Numerical Simulations of Ice Particle Transport at Representative Turbofan Compressor Conditions

Engine icing threatens compressor operation and service life. Ice crystal ingestion at cruise and descent phases of flight result in smaller, partial melted crystals entering the engine core. Here, crystals can stick to stationary surfaces driven by the presence of a water film, and evaporative and melting heat exchange with the mixed phase crystals. Modelling of the ice crystal cloud conditions is needed to understand threat areas within the core and operating envelope and to provide a reliable basis for ice accretion modelling at solid surfaces. A particle transport model in three-dimensions combining tracking, heat transfer, phase change along with a turbophoresis model is presented for non-spherical mixed phase ice crystals. These present a challenge to model effectively considering the complex and anisotropic geometries of ice crystals. Further, crystals can fragment, melt and agglomerate along the gas path. This affects heat transfer, phase change and ice porosity which will implicate the deposition location and composition. The model is validated against previous altitude icing wind tunnel experiments at LP/IP compressor operating conditions. Measured conditions for ice crystal mass flux provide experimental comparison against particle advection and phase change. Particle advection is modelled using an Euler-Lagrangian approach with two-way mass-energy coupling. Particle turbulent dispersion is modelled using a discrete random walk (DRW) model which is appropriate for flows where particles are primarily inertially-moderated. The model is seen to predict particle cloud mass distribution to within 15% of the experimentally measured total water content (TWC). Particle sizes between 2 μm and 131 μm and are modelled as spheroids. The variation in melt response is investigated relative to particle size and aspect ratio. High aspect ratio particles (AR > 10) result in 5% to 20% phase change augmentation depending on the particle angle of attack. Two way coupling is shown to increase the melt ratio by up to 10% and reduce the total water content by up to 25% compared to one-way coupling. The model provides a framework for compressor stage ice particle transport and deposition in ice crystal icing conditions.