Ingestion of high-altitude ice particles can be hazardous to aircraft engines in flight. Ice accretion may occur in the compression system, leading to blockage of the core gas path, blade damage and/or engine flameout. Numerous engine powerloss events since 1990 have been attributed to this mechanism. An expansion in engine certification requirements to incorporate ice crystal conditions has spurred efforts to develop analytical models for phenomenon. A necessary component of a complete icing simulation is a thermodynamic accretion model. In this paper, a new model for ice crystal icing is developed through adaptation of the Extended Messinger Model (EMM) from supercooled water conditions to mixed phase conditions (ice crystals and supercooled water). The new model is termed the Extended Messinger Model -Crystals (EMM-C). Continuity and energy balances are performed using the local flow conditions and impinging mass fluxes of ice and water. For accretions grown on a warm engine surface, initially above freezing temperature, a novel three-layer (water-ice-water) accretion structure is proposed, and the underlying equations described. Finally, predictions from the EMM-C model are compared to experimental results generated in an ice crystal wind tunnel. Compared with current literature icing models, EMM-C provides a tractable framework for modelling engine icing through allowing mixed phase accretions on warm surfaces.

Numerous turbofan power loss events caused by the ingestion of high altitude ice crystals have been reported, causing significant concern to the aviation industry. In recent years, experiments have been conducted to explore the physics behind the accretion process, with the aim of producing numerical models to predict the ice growth. Validation of such models require accurate measurement of three-dimensional ice accretion profiles in more engine realistic applications. To date multi-camera two-dimensional views and gom scanning has been utilised. This paper details the first application of DIP for measuring the transient growth of three dimensional ice crystal accretion profiles. This uses laser grid patterns projected onto the surface of interest and conventional cameras mounted at a different viewing angle to the laser. This method was tested in an altitude ice crystal tunnel, using a prismatic stator blade test piece. Comparison of the DIP results to traditional backlit views and a commercial scanner showed that it was possible to measure ice crystal icing accretion thickness’s with an accuracy of 0.5 mm.

Fully glaciated ice crystals can be ingested into aero engines, partially melt through the first few stages of compressors and eventually cause large accretions on stationary components. Ice crystals pose a threat due to damage caused by ice shedding. With regulators expanding certification of engines to include the threat of ice crystals, there has been significant research at both the fundamental and complete engine tests. This paper details experiments which lay somewhere between the these two ends of the spectrum; an engine representative stationary geometry with direct control and measurement of the inlet icing conditions. The aim of the experiments is to directly measure ice thickness on complex three dimensional surfaces of a combined linear cascade and swan neck duct. This will enhance our understanding of locations at which there is a large threat to ice accretion and at what conditions this occurs. This paper will detail the test piece geometry, present the results of the experimental campaign and initial analysis and conclusions from the experiments.

It has been recognized in recent years that high-altitude atmospheric ice crystals pose a threat to aircraft engines in flight. It is believed that ice can accrete inside the core compressor, although the mechanism by which this occurs remains poorly understood. To model ice crystal accretion, an estimate of the proportion of the impinging ice and water that sticks to a surface (the sticking efficiency) is required. This Paper presents data from experiments undertaken using an axisymmetric test article in an altitude ice crystal wind tunnel. A 35 deg half-angle nose was used for a parametric study of Mach number, total water content, wet bulb temperature, and particle size distribution. An assessment of the response of a multiwire probe used for measuring liquid water content is also presented. A shadowgraphy technique was used to measure the ice accretion growth rate on the nose. The results show that sticking efficiency has a strong dependency on particle melt ratio. Erosion is shown to be correlated with particle size, Mach number, and surface angle. New semi-empirical models are presented for sticking probability and erosion.

High altitude ice crystals can pose a threat to aircraft engine compression and combustion systems. Cases of engine damage, surge and rollback have been recorded in recent years, believed due to ice crystals partially melting and accreting on static surfaces (stators, endwalls and ducting). The increased awareness and understanding of this phenomenon has resulted in the extension of icing certification requirements to include glaciated and mixed phase conditions. Developing semi-empirical models is a cost effective way of enabling certification, and providing simple design rules for next generation engines. A comprehensive ice crystal icing model is presented in this paper, the Ice Crystal Icing ComputationaL Environment (ICICLE). It is modular in design, comprising a baseline code consisting of an axisymmetric or 2D planar flowfield solution, Lagrangian particle tracking, air-particle heat transfer and phase change, and surface interactions (bouncing, fragmentation, sticking). In addition, an efficient particle tracking method has been developed into the code, which employs the representative particle size distribution at each injection location and a deterministic particle sticking method by using an in-situ particle based scaling factor without aborting the particle trajectories. Various time integration algorithms, including implicit and explicit Euler and Runge-Kutta methods, are discussed and the effect on an acceptable timestep investigated. The model then improves on those available in the literature in three ways: firstly, an adaptation of the Extended Messinger Model (EMM) to mixed phase conditions is incorporated, improving the fidelity of the ice accretion prediction compared with the classical Messinger model. Secondly, an experimentally-derived model for sticking efficiency improves the accuracy of the continuity equation in the EMM; thirdly a simple model for integrating two-way coupling of mass and energy is proposed.

Numerous turbofan power-loss events have occurred in high altitude locations in the presence of ice crystals. It is theorized that ice crystals enter the engine core, partially melt in the compressor and then accrete onto stator blade surfaces. This may lead to engine rollback, or shed induced blade damage, surge and/or flameout. The first generation of ice crystal icing predictive models use a single flow field where there is no accretion to calculate particle trajectories and accretion growth rates. Recent work completed at the University of Oxford has created an algorithm to automatically detect the edge of accretion from experimental video data. Using these accretion profiles, numerical simulations were carried out at discrete points in time using a manual meshing process. That work showed that flow field changes caused by a changing accretion profile had significant effects on the collection efficiency of impinging particles, ultimately affecting the mass of accreted ice and its shape. This paper discusses the development of the ICICLE numerical ice crystal icing code to include a fully automated two-way coupling between the accretion profile and flow field solution, to account for these effects. The numerical strategy; geometry redefinition, mesh update and flow field solution are discussed, followed by a comparison to experimental ice accretion of a simple 2D geometry and model predictions with and without flow field updating. The results showed that significant changes in leading edge accretion profiles were numerically predicted when the only the geometry was updated. Further changes then occurred when the flowfield was also updated.

A significant number of historical engine powerloss events have recently been attributed to ingestion of high altitude ice crystals, prompting regulators to expand engine certification envelopes to incorporate 'ice crystal icing' conditions. There has been a resulting effort by OEMs and academia to develop analytical and semi-empirical models for the phenomenon, partly through use of rig testing. The current study presents results and analysis of experiments conducted in the National Research Council's Research Altitude Test Facility (RATFac). The experiments used a simplified compressor stator vane test article, designed to produce data to build semi-empirical models and validate an existing ice crystal icing code. Accretion growth rates, extracted from backlit shadowgraphy, are presented as a function of test condition, and the algorithm of a new image processing technique using Canny filtering is discussed. Wet bulb temperature, Mach number, particle size and test article angle of attack were systematically varied. In line with previous experiments, the accretion growth rate was observed to be strongly dependent upon bulk particle melt ratio, with a peak growth rate at approximately 10% melt ratio. If leading edge accretions shed during the test, the growth rate of the second accretion would be greater than the first, regardless of test condition, due to the cooling of the substrate surface during the first accretion. The rate of erosion was found to correlate with bulk particle kinetic energy. The highest growth rates were observed for positive angles of attack, at both the leading edge and pressure surface. In contrast, at negative angles of attack growth rates were minimized, attributed to unfavourable accretion conditions on the suction surface. Finally, a qualitative assessment of the accretion quality and build/shed behavior as a function of test condition is presented.