Ice crystal icing is still an ongoing threat to aviation, especially but not limited to jet engines. The impact of ice crystal icing on engine performance has been analyzed by synthesis using performance models matched to measured engine data. This complex and costly approach is mostly a phenomenological one which often excludes the possibility to derive a fundamental physical model of the process. However, due to the intrinsic realistic nature, data obtained from engine or component testing may serve as a source of boundary conditions and validation data.

Fundamental, less complex research has been conducted on simple geometries using uniform boundary conditions, derived from averaged engine data or mean-line calculations. The ease of instrumentation and the potential to experimentally differentiate specific phenomena, facilitate the derivation of fundamental physical models. This comes at the expense of the geometry as well as aero- and thermodynamic conditions not being representative of a realistic engine environment.

In order to bridge the gap between phenomenological and fundamental research and in order to bundle the respective advantages, there is a need for an experimental environment that provides engine-like conditions at low cost, which enables application of versatile measurement instrumentation.

The Institute of Aircraft Propulsion Systems of the University of Stuttgart has developed a linear compressor cascade test rig, which is intended to be tested in the Altitude Test Facility (ATF) enabling experiments over a broad range of engine-like operating conditions. The test points are to be selected based on engine realistic conditions simultaneously warranting the occurrence of localized ice accretion.  In this context, the existence of a set of thermodynamic and aerodynamic parameters being indicative of a potential localized icing risk under realistic operating conditions is investigated. A numerical model of the first stage of the NASA Stage 67 is used for the analysis, representing the geometry and characteristic traits of a modern turbofan engine. The operating and environmental conditions are chosen to simulate climb conditions with constant non-dimensional power setting through ascending parcels of moist air. Due to high engine operating points, the climb is supposed to be more susceptible to ice crystal icing. The flow solution is generated using the ANSYS CFX flow solver. The droplet and ice crystal calculations are performed with the ANSYS FENSAP-ICE solver suite.

The results are depicted in a newly conceived diagram aggregating environmental and localized thermodynamic conditions. This diagram allows for graphical representation of upper and lower icing limits, confining the range of experimental test points. The diagram is based on averaged or integral data computed from high fidelity CFD and performance data. The averaging enables the data to be used in a test rig environment with uniform boundary conditions or in lower fidelity codes.    

Neglecting heat transfer through particle impact and assuming an adiabatic compressor, a local total wet bulb temperature around freezing constitutes the lower temperature limit for ice accretion resulting from ice crystal icing. Based on experimental observation and model synthesis, several investigators have used the local static wet bulb temperature in combination with local particle melting ratios and water-to-air mass flow ratios as a measure of icing risk, for condition scaling purposes and as lower and upper temperature limit for ice accretion. However, the results of the present numerical study indicate, that the range of the local static wet bulb temperatures presented by other investigators are in general an imperfect measure for the anticipation of a regional icing risk in the melting-dominated regime.

Based on this observation the paper aims to investigate the existence of an adequate general upper icing limit for a prescribed engine operating point. The lower and the upper limit are used to determine the range of experimental test points.


Boundary Conditions for Compressor Cascade Ice Crystal Icing Testing

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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