Purge air is injected through seals in the hub and shroud of axial turbines in order to prevent hot gas ingestion into the inter-stage gaps. An investigation into the losses involved with the injection of purge air has been undertaken, with the objectives of answering where the losses are generated, how they are generated, and what are the most effective ways for reducing them. In order to address these questions, a consistent framework for interpreting entropy generation as a measure of loss is developed for turbomachinery applications with secondary air streams. A procedure for factoring out distinct effects is also presented. These tools, applied to steady computations, elucidate four mechanisms by which change in loss generation is brought about due to injection of purge air: a shear layer between purge and main streams, interaction with the passage vortex system that generates radial velocity gradients, changes in wetted loss and tip clearance flow due to an increased degree of reaction, and the potential for reducing tip clearance flow for the case of purge flow injected from the shroud. An emphasis is placed on tracing these effects to specific purge flow characteristics that drive them. The understanding gained provides a rationale for the observed sensitivity of purge flow losses to the design parameters purge air mass fraction and swirl, compared to purge slot axial inclination and gap width. Preswirling of purge flow is less effective in mitigating losses in the case of shroud-injection, since there is a tradeoff with the tip clearance flow suppression effect.
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e-mail: zlatinov@alum.mit.edu
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November 2012
Research Papers
Turbine Hub and Shroud Sealing Flow Loss Mechanisms
Metodi Blagoev Zlatinov,
Metodi Blagoev Zlatinov
Gas Turbine Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
e-mail: zlatinov@alum.mit.edu
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Choon Sooi Tan,
Choon Sooi Tan
Gas Turbine Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
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Matthew Montgomery,
Matthew Montgomery
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
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Tito Islam,
Tito Islam
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
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Melissa Harris
Melissa Harris
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
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Metodi Blagoev Zlatinov
Gas Turbine Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
e-mail: zlatinov@alum.mit.edu
Choon Sooi Tan
Gas Turbine Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
Matthew Montgomery
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
Tito Islam
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
Melissa Harris
Gas Turbine Engineering, Siemens Energy Inc., Orlando, FL 32826
J. Turbomach. Nov 2012, 134(6): 061027 (12 pages)
Published Online: September 4, 2012
Article history
Received:
July 17, 2011
Revised:
July 22, 2011
Online:
September 4, 2012
Published:
September 4, 2012
Citation
Zlatinov, M. B., Sooi Tan, C., Montgomery, M., Islam, T., and Harris, M. (September 4, 2012). "Turbine Hub and Shroud Sealing Flow Loss Mechanisms." ASME. J. Turbomach. November 2012; 134(6): 061027. https://doi.org/10.1115/1.4006294
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