Thesis (Ph. D.)--University of California, Davis, 2004. / Degree granted in Molecular, Cellular, and Integrative Physiology. Includes bibliographical references. Also available via the World Wide Web. (Restricted to UC campuses)

Thesis (Ph.D.) - University of St Andrews, April 2010.

Thesis (Ph. D.)--Montana State University--Bozeman, 2006. / Typescript. Chairperson, Graduate Committee: Jay J. Rotella. Includes bibliographical references.

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 83-90). Description: xii, 90 leaves : ill. ; 29 cm.

Advanced rotating shaft seals have the potential to significantly increase the efficiency and performance of steam and gas turbines. Two such seals, brush and leaf seals, rely on the use of thousands of flexible filaments to close clearances between rotating components and their static casings. The current life of the components is poor compared to the rest of the gas turbine, limiting the seals' deployment, particularly in the jet engine at high temperature and pressure. Poor understanding of the seal installation response to frictional heat generated at the point of filament-rotor contact during operation has limited the ability to predict engine closures and hence seal behaviour and life. The resulting temperature rises may compromise the mechanical integrity of the engine rotor in extremis leading to a shaft failure. This thesis considers the heat transfer mechanisms that govern frictional heating, of both the fluid and solid components in the vicinity of such seals, characterising the process both experimentally and using numerical models. Through the identification of key features of the heat transfer a simple numerical methodology is shown to predict the thermal behaviour of the seal installation sufficiently accurately for engine design purposes. A low order heat transfer model, using a simple electrical analogy for heat transfer is used to investigate frictional heat generation. When contact occurs between the rotor surface and the seal filaments, mechanical energy is dissipated as heat at the interface. This is conducted into the rotor and the seal filaments in proportions that depend on the heat transfer characteristics of both contacting bodies (thermal resistances). To calculate the heat partition ratio and the resulting contact temperature, the thermal resistances of both rotor and seal need to be known. To that end, a new test facility, the Seal Static Thermal Test Facility (SSTTF), is developed. This is first used to study the convective heat transfer occurring in the vicinity of the seal; heat transfer coefficients based on appropriate, scalable, gas reference temperatures are reported. Importantly the results show a larger area on the rotor surface affected by the presence of the seal than was assumed by previous workers. The test rig is further modified to generate heating in a static test rig equivalent to the frictional heating at the filament tips. The test rig allows the contact temperature between rotor and seal, a critical previously unknown parameter to be measured in a well-conditioned environment. The presence of many thousands of vanishingly small flow passages in filament seals makes their explicit modelling unfeasible for engine design purposes. Thus the results from the experimental campaign are used to develop a simple computational fluid dynamic model of the seal, including empirically derived frictional heating, and seal porosity models, to achieve similar leakage and surface heat transfer to the rotor as was seen in the static experiments. The low order CFD methodology presented in the thesis is finally employed to model the transient operation of a brush seal under engine representative rotor surface speeds and differential pressures. Experimental data were generated in the Oxford Engine Seal Test Facility for a typical brush seal rubbing against a high growth rotor. These experiments were modelled using CFD and finite element analysis using parameters derived from static tests for the porous modelling of the seal leakage. Comparison of results shows that, without further tuning, the thermal behaviour is captured well with a moderate conservative overestimation of rotor heating with increased differential pressure across the seal allowing the strategy to be used as an engine design tool.

A conceptual model is proposed that describes the dynamics of the Pribilof Islands North Pacific fur seal (Callorhinus ursinus). It is suggested that fur seals are regulated most strongly at population levels close to the limits set by the availabilities of food and breeding space. Population growth appears to be primarily regulated by changes in the rates of survival, reproduction, and dispersal of young animals. The proposed conceptual model is used to shape a mathematical formulation that incorporates basic fur seal life history features. The simulation analysis is able to explain the decline of the Pribilof Islands population by reconstructing pup estimates and counts of adult males over the period 1950 to 1980. Simulation results show that commercial female harvesting and a series of poor juvenile survival rates were responsible for the observed decline in pup production on Saint Paul Island. The lower number of bulls counted during the last two decades can be accounted for if adult male survival was higher during the 1950s. The decline in adult male survival, possibly due to debris entanglement, does not appear to be equally true of females. The major driving variable of the fur seal system and the key factor that accounts for the overall decline of the Pribilof herd is the survival of juveniles. In this regard, the continued population decline through the 1980s appears to be maintained by exogenous factors that are independent of current management practices. Model results are considered reliable if simulation parameters (particularly adult survival) contain little error. A detailed procedure for analysing the sensitivity of model output to errors in simulation parameters is described in an adjoining appendix as is a revised procedure for estimating the survival of juvenile fur seals. The thesis concludes with recommendations for future research. / Science, Faculty of / Zoology, Department of / Graduate

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