Swati Saxena

Modeling and Analysis of Ice Shed in Multistage Compressor of Jet Engines

Simulation of ice shed into a multistage axial compressor involves a coupled two phase flow of a continuous phase comprising of air and water vapor and a discrete phase with ice crystals and water droplets. A first principles based discrete phase model is formulated to capture the heat and mass transfer processes of ice flow in air. A quasi one-dimensional model is used to represent the continuous phase. An exchange of information at every time step between the two models leads to a coupled response that alters characteristics like temperature and pressure distributions across the compressor. However, an understanding of the impact of various assumptions used for modeling of the icing physics is imperative in order to establish the fidelity of the developed icing model, before its use in gas turbine engine ice ingestion studies. This paper describes the assumptions and semi-numerical models used in the coupled discrete-continuous phase flow numerical models. The input characteristics of the discrete phase related to the size and distribution of ice crystals, the assumed percentage of ice particles escaping through compressor bleed ports, simplifications associated with ice and droplet breakup on impact with compressor blades, moisture content affecting the dry air properties, are some of the factors that are variables in the icing study. The impact of these factors on the compressor flow dynamics is estimated through a parametric analysis.

Transient Behavior in Axial Compressors in Event of Ice Shed

Incidents of partial or total thrust loss due to engine icing at cruise have been recorded over past several years. These events increase the demand for better understanding of compressor dynamics under such conditions. In the present study, physics based compressor blade row model (BRM) is used to evaluate the effect of booster ice-shed on axial high pressure compressor (HPC) at flight and approach idling conditions (65%–82% Nc). A representative aviation high-bypass turbofan engine HPC is used in this study. Transient behavior of compressor with varying ice ingestion conditions is compared and inter-stage dynamics is analyzed. Stage re-matching occurs due to heat exchange between air and ice which dictates the stall inception stage in the compressor. It is found that although T3 drop is closely related to compressor stall inception, the transient mechanism of ice-shed also plays an important role. Comparisons are made with steady energy balance equation to determine total water content (TWC) at HPC inlet to emphasize the importance of compressor transients. The ice amount, its ingestion duration and rate affect the onset of stall. HPC might sustain through a slower ice-shed while a faster ice-shed can lead to compressor stall with little or no chances of recovery. Understanding this transient behavior and inter-stage dynamics due to ice-shed will help in designing and implementing passive or active stall control mechanisms.© 2015 ASME

Analysis of Stall Onset in a Multistage Axial Flow Compressor in Response to Engine Icing

Propulsion system instabilities such as compressor surge and stall can arise due to ice ingested by an aircraft engine flying through high ice water content regions. Performance and operability are affected by ice ingestion into a gas turbine engine compression system. Since the 1980’s ingestion of ice particles into engines have caused over one hundred engine power loss events. This paper presents an analysis of a multistage compressor system response to ice ingestion. Towards this, an aero-thermodynamic model of the discrete particles that captures mass and heat balances with air, is constructed. The computational methodology integrates it with a quasi-one-dimensional unsteady flow model with additional source terms from the discrete phase. From numerical simulations of the coupled continuous-discrete phase flow model, it is observed that a re-matching of the stages across the compressor occurs with increasing ice flow rates to accommodate loss of energy to the ice flow. The axial flow and pressure oscillations with increasing ice flow rates results in an eventual irretrievable unsteady compressor operating point excursion to stall side. The flow solver simulates the onset of a surge-stall event and identifies the stalling stage of the compressor. The numerical simulations correlate the magnitude of ice flow rates to pressure disturbances ultimately causing compressor instability.