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Secondary air interaction with main flow in axial turbines

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dc.contributor.advisor Choon S. Tan. en_US Zlatinov, Metodi B. (Metodi Blagoev) en_US
dc.contributor.other Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. en_US 2011-11-18T19:30:18Z 2011-11-18T19:30:18Z 2011 en_US 2011 en_US
dc.description Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. en_US
dc.description This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. en_US
dc.description Cataloged from student submitted PDF version of thesis. en_US
dc.description Includes bibliographical references (p. 155-157). en_US
dc.description.abstract Secondary air, known as purge air, is injected through seals in the hub and shroud of axial turbines to prevent hot gas ingestion into the endwall cavities. An investigation into the interaction of purge ow with turbine main ow has been undertaken, to determine where losses are generated, how they are generated, and what are the most eective ways for reducing them. The eect of purge ow design on the system's susceptibility to ingestion was also studied. Tools developed for accomplishing these objectives include: a consistent framework for isolating entropy generated due to viscous effects, a procedure for factoring out individual loss categories, and a linear model for secondary air ow response to the main flow pressure field. These tools, applied to steady computations, elucidate four routes through which change in loss generation is brought about by purge air injection: a shear layer between purge and main streams, modification of the secondary ow through the blade passage, an increase in degree of reaction, and the potential for reducing tip clearance ow (for the case of purge ow injected from the shroud). It was further determined that purge air mass ow and swirl velocity are eective parameters for mitigating loss, with a potential for 70% reduction in purge ow losses. By contrast, purge slot axial inclination and gap width do not affect the loss characteristics of purge ow by more than 6%. The benet of pre-swirling purge ow can be negated by decreased sealing effectiveness, if ingestion is driven by the pressure non-uniformity associated with the rotor upstream in influence. However for a representative vane-rotor stage, in which the vane-induced circumferential pressure non-uniformity dominates in the intra vane-rotor gap, pre-swirling purge flow can be beneficial to deterring hot gas ingestion. Finally a framework has been formulated for assessing the time-averaged impact of unsteady vane-rotor interaction on purge ow-induced loss generation. Preliminary results suggest that ow unsteadiness can result in substantially higher losses associated with purge flow injection. en_US
dc.description.statementofresponsibility by Metodi B. Zlatinov. en_US
dc.format.extent 157 p. en_US
dc.language.iso eng en_US
dc.publisher Massachusetts Institute of Technology en_US
dc.rights M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. en_US
dc.rights.uri en_US
dc.subject Aeronautics and Astronautics. en_US
dc.title Secondary air interaction with main flow in axial turbines en_US
dc.type Thesis en_US S.M. en_US
dc.contributor.department Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. en_US
dc.identifier.oclc 758677984 en_US

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