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Research Papers

The Effects of Blade Passing on the Heat Transfer Coefficient of the Overtip Casing in a Transonic Turbine Stage

[+] Author and Article Information
Steven J. Thorpe

Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough LE12 7TW, UKs.j.thorpe@lboro.ac.uk

Roger W. Ainsworth

Department of Engineering Science, University of Oxford, Oxford, UK

J. Turbomach 130(4), 041009 (Jul 31, 2008) (8 pages) doi:10.1115/1.2776950 History: Received August 18, 2006; Revised January 10, 2007; Published July 31, 2008

In a modern gas turbine engine, the outer casing (shroud) of the shroudless high-pressure turbine is exposed to a combination of high flow temperatures and heat transfer coefficients. The casing is consequently subjected to high levels of convective heat transfer, a situation that is complicated by flow unsteadiness caused by periodic blade-passing events. In order to arrive at an overtip casing design that has an acceptable service life, it is essential for manufacturers to have appropriate predictive methods and cooling system configurations. It is known that both the flow temperature and boundary layer conductance on the casing wall vary during the blade-passing cycle. The current article reports the measurement of spatially and temporally resolved heat transfer coefficient (h) on the overtip casing wall of a fully scaled transonic turbine stage experiment. The results indicate that h is a maximum when a blade tip is immediately above the point in question, while the lower values of h are observed when the point is exposed to the rotor passage flow. Time-resolved measurements of static pressure are used to reveal the unsteady aerodynamic situation adjacent to the overtip casing wall. The data obtained from this fully scaled transonic turbine stage experiment are compared to previously published heat transfer data obtained in low-Mach number cascade-style tests of similar high-pressure blade geometries.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic diagram showing the axial positions of the casing heat transfer instrumentation (numbers refer to axial chord)

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Figure 2

Schematic diagram of the heat transfer instrumentation (showing Peltier installation)

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Figure 3

The time-resolved heat transfer rate at various axial locations as a function of blade-passing phase (green line indicates blade suction surface, and red line the blade pressure surface)

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Figure 4

The time-resolved heat transfer coefficient at various axial locations as a function of blade-passing phase (green line indicates blade suction surface, and the red line the blade pressure surface)

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Figure 5

The time-resolved adiabatic wall temperature at various axial locations as a function of blade-passing phase (green line indicates blade suction surface, and the red line the blade pressure surface)

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Figure 6

Contour plots of the time-resolved conditions on the overtip casing wall: (a) heat transfer rate, (b) heat transfer coefficient, and (c) adiabatic wall temperature

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Figure 7

A schematic diagram illustrating typical flow vectors in the blade-tip region

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Figure 8

A contour plot of the time-resolved casing static pressure

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