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Development of an ice accretion code suitable for mixed-phase icing conditions

Bullee, P.A. (2015) Development of an ice accretion code suitable for mixed-phase icing conditions.

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Abstract:Ice formation on aircraft, or simply aircraft icing, is since long been recognized as a threat towards safe aircraft operation. It is the result of meteorological circumstances and an important object of study in the field of aeronautics. It has only been since the beginning of this century that meteorological and accident investigation revealed that aircraft engines are also vulnerable to icing conditions. When large amounts of ice crystals enter the engine, they can form a heat sink and accrete on the cooler parts inside the engine. Especially the first stages of the compressor, where the temperature is around the freezing temperature of water, are sensitive to these phenomena. Current ice accretion prediction models are not suited to describe these phenomena. Traditionally, icing is caused by supercooled liquid droplets naturally present in the air. In the case of engine ice accretion, ice crystals, which are also naturally present in the air, also play an important role. Icing codes are based on the principle of the Messinger model, a one-dimensional equilibrium energy balance, which uses the equilibrium temperature of a surface to study ice growth. Impact parameters for the Messinger model include a particle impingement distribution on the surface. This distribution is determined from the trajectories of the ice crystals and water droplets in the flow around an obstacle. This distribution is a measure for the amount of mass that impacts the surface and is the input for the energy and mass balance on the surface. From the energy and mass balance the surface temperature and the thickness of the accreted ice layer can be solved. Ice crystals show a different behaviour from supercooled liquid water droplets. Upon impact with a surface they are expected to either fully rebound and remain intact, scatter and partly rebound or fully scatter without rebounding. Parameters important in this process are the kinetic energy and the size of a particle, but also the condition of the surface. A surface can be covered with ice, water or with neither of them. Ice crystals impacting a surface covered with ice can lead to erosion. Water on the surface can be splashed by the impacting surface and ice crystals impacting a dry surface are expected to bounce. A mixed-phase ice accretion prediction code has been developed in the research described in this report. This code assumes that al the particles stick to the surface upon impact. The erosive action is accounted for by an empirical model that effectively reduces the amount of impinging ice crystals. The phenomena of mass evaporation from the surface have been revised. The influence of these phenomena is shown to be only minor. In the context of an European project, the High Altitude Ice Crystals Consortium, a number of ice accretion codes have been extended to mixed-phase icing conditions. These extended codes are analysed and used together with the results from wind tunnel experiments to compare results generated by the newly developed code. A number of test cases do give results comparable to the numerical results from other codes, whereas other results are quite different. The aim of this research was however to develop a generally applicable mixed-phase icing model. The codes from which results were compared in this report had either a limited range of application or were built upon a large basis of expertise in ice accretion modelling. From the tests performed with the newly introduced accretion model is concluded that the mechanisms of erosion and particle impingement are very important for a mixed-phase ice accretion code. In order to build a more accurate ice accretion model, it is therefore strongly suggested that these mechanisms are researched and taken into account in an updated version of the current mixed-phase ice accretion model.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:33 physics, 52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/86207
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