Engine Icing Modeling and Simulation (Part I): Ice Crystal Accretion on Compression System Components and Modeling its Effects on Engine Performance 2011-38-0025

During the past two decades the occurrence of ice accretion within commercial high bypass aircraft turbine engines under certain operating conditions has been reported. Numerous engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion such as degraded engine performance, engine roll back, compressor surge and stall, and even flameout of the combustor. As ice crystals are ingested into the engine and low pressure compression system, the air temperature increases and a portion of the ice melts allowing the ice-water mixture to stick to the metal surfaces of the engine core. The focus of this paper is on estimating the effects of ice accretion on the low pressure compressor, and quantifying its effects on the engine system throughout a notional flight trajectory. In this paper it was necessary to initially assume a temperature range in which engine icing would occur. This provided a mechanism to locate potential component icing sites and allow the computational tools to add blockages due to ice accretion in a parametric fashion. Ultimately the location and level of blockage due to icing would be provided by an ice accretion code. To proceed, an engine system modeling code and a mean line compressor flow analysis code were utilized to calculate the flow conditions in the fan-core and low pressure compressor and to identify potential locations within the compressor where ice may accrete. Note that there is a baseline value of aerodynamic blockage due to low velocity air near the compressor inner and outer walls and blade surfaces (boundary layer blockage). There is also a blockage due to the blade metal thickness. In this study, the “additional blockage” refers to blockage due to the accretion of ice on the metal surfaces. Once the potential locations of ice accretion are identified, the levels of additional blockage due to accretion were parametrically varied to estimate the effects on the low pressure compressor blade row performance operating within the engine system environment. This study includes detailed analysis of compressor and engine performance during cruise and descent operating conditions at several altitudes within the notional flight trajectory. The purpose of this effort is to develop the codes to provide a predictive capability to forecast the onset of engine icing events, such that they could help in the avoidance of these events.

It has been reported that ice crystal accretion in gas turbine engines is dependent on the amount of mixed phase conditions (liquid and solid) that exist. In addition, the problem of ice accretion is highly multi-disciplinary, since it involves heat transfer from the air to the compressor metal surfaces. The first phase of this study focuses on addressing the thermodynamic cycle through the engine system code and the mean line flow analysis through the compressor through a flight trajectory. The second phase of this study focuses on the ice particle physics in the flow field that was computed in the first phase.