A Three-Layer Thermodynamic Model for Ice Crystal Accretion on Warm Surfaces: EMM-C

Abstract

Ingestion of high altitude atmospheric ice particles can be hazardous to gas turbine engines in flight. Ice accretion may occur in the core compression system, leading to blockage of the core gas path, blade damage and/or 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, as a method of demonstrating safe operation. A necessary component of a complete analytical icing model is a thermodynamic accretion model. Continuity and energy balances are performed using the local flow conditions and the mass fluxes of ice and water that are incident on a surface to predict the accretion growth rate. In this paper, a new thermodynamic model for ice crystal accretion is developed through adaptation of the Extended Messinger Model (EMM) from supercooled water conditions to mixed phase conditions (ice crystal and supercooled water). A novel three-layer accretion structure is proposed and the underlying equations described. The EMM improves upon the original model for airframe icing, the Messinger Model, by permitting a linear temperature gradient through the ice and water layers. This in turn allows prediction of the time over which water exists in isolation on an initially warm surface, before an ice layer forms. This is of particular interest to engine icing, as surfaces may initially be significantly above freezing temperature, before cooling on exposure to ice particles. The method is solved in a multi-step approach, where the overall exposure time is divided into discrete windows, and the calculation performed over each window. This allows the local flow conditions to be updated between windows, permitting the incorporation of a reducing flow enthalpy due to particle evaporation, as well as transient engine operation. Model results are then compared to experimental results. Comparisons are made to solutions generated using the standard Messinger Model.

Two-Way Flow Coupling in Ice Crystal Icing Simulation

“…Finally, a three-layer Extended Messenger Model is applied to determine the ice growth. The overall model is discussed in greater detail in [2], and the Messenger model details can be found in [8].…”

“…The model incorporates Lagrangian particle tracking, a two-way heat transfer and phase change model, bouncing, sticking and fragmentation models, and a thermodynamic accretion model based on an Extended Messinger Model which includes a three layer model for blade temperatures above 00C. Details of the complete model may be found in [2] and details of the thermodynamic accretion model in [3]. In the standard model, a flow field solution is imported and is unchanged throughout the simulation time (a 'frozen' flow field).…”

“…This simplification is also made in the first generation of ice crystal icing models -for example that of ONERA [4], Wright et al [5] and Nilamdeen & Habashi [6]. However, testing in ice crystal wind tunnels has shown accretion size after an exposure time of minutes may be of the same order of magnitude -or greater -as the characteristic dimension of the test article (such as the chord of a blade or diameter of an axisymmetric model) [3,7]. Recent testing of the Honeywell ALF502-R5 engine at NASA's PSL-3 altitude ice crystal test facility showed that blockage of stator passages in the LP booster stage of the compressor could reach 60% [9].…”