Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

John R Saylor, Committee Chair

Committee Member

Yiqiang Han

Committee Member

Joshua Bostwick

Abstract

Aircraft engine icing has emerged as one of the greatest threats to safe operation of aircrafts today contributing to more than half of all the aircraft icing accidents reported between 1990-2000. Engine icing mostly occurs in the low-pressure compressor section of the engine where ice particles entering the engine undergo partial or complete melting on encountering warm surfaces. These partially melted crystals cool the engine parts until the freezing point of water is reached. Further accumulation of ice inside the engine leads to ice accretion and shedding. This situation may lead to complete power loss in the engine and acts as an operational hazard for the aircraft. This study aims at creating mathematical models for the two fundamental processes that occur during aircraft engine icing namely: melting of ice particles and freezing of water films. To understand the melting behavior of ice particles, a two-layer model was developed and the governing equations for the heat balance at the surface of the particle and the surface of the melting ice core were defined. The physical parameters affecting the melting behavior of the ice particle were identified and their unsteady effects introduced in the model to obtain a final relation between radius reduction ratio and melt time. The analytical model was then validated by comparing the melting rate and melt time data obtained from an experiment conducted by Dr. Jose Palacios and Sihong Yan at Pennsylvania State University for observing melting of isolated levitated ice particles ranging from 300μm to 1200μm in size. From the comparison it was found that the two-phase model developed in this research correctly predicts melting rate and melt times for ice particles greater than 800μm with an average absolute melt time error of 4%.

The goal of the next part of the research was to obtain a mathematical expression for the latent heat flux at the surface on which freezing of a water film takes place. For this the two-phase Stefan problem approach was applied to a water film undergoing freezing at a constant temperature freezing surface and an insulated water surface. The explicit solution obtained for the Stefan problem was then used to obtain temperature profiles for the varying ice and water layers. The latent heat flux at the freezing surface was derived and validated against a heat flux measurement reading from a similar experiment.

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