Analysis of Airfoil Trailing Edge Heat Transfer and Its Significance in Thermal-Mechanical Design and Durability

[+] Author and Article Information
F. J. Cunha, M. T. Dahmer

Pratt & Whitney, United Technologies Corporation, East Hartford, CT 06108

M. K. Chyu

Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA 15261mkchyu@engr.pitt.edu

J. Turbomach 128(4), 738-746 (Feb 01, 2005) (9 pages) doi:10.1115/1.2220047 History: Received October 01, 2004; Revised February 01, 2005

The trailing edge section of modern high-pressure turbine airfoils is an area that requires a high degree of attention from turbine performance and durability standpoints. Aerodynamic loss near the trailing edge includes expansion waves, normal shocks, and wake shedding. Thermal issues associated with trailing edge are also very complex and challenging. To maintain effective cooling ensuring metal temperature below design limit is particularly difficult, as it needs to be implemented in a relatively small area of the airfoil. To date, little effort has been devoted to advancing the fundamental understanding of the thermal characteristics in airfoil trailing edge regions. Described in this paper are the procedures leading to closed-form, analytical solutions for temperature profile for four most representative trailing edge configurations. The configurations studied are: (1) solid wedge shape without discharge, (2) wedge with slot discharge, (3) wedge with discrete-hole discharge, and (4) wedge with pressure-side cutback slot discharge. Comparison among these four cases is made primarily in the context of airfoil metal temperature and resulting cooling effectiveness. Further discussed in the paper are the overall and detail design parameters for preferred trailing edge cooling configurations as they affect turbine airfoil performance and durability.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Typical shock structures in high-pressure turbine airfoils: (a) from Kuhne (8), and (b) from Eisemann (9)

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Figure 2

Trailing edge analytical model without internal convective cooling

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Figure 3

Trailing edge model with centerline slot

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Figure 4

Trailing edge model with cooling holes

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Figure 5

Cut-back trailing edge model with slots

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Figure 6

Metal temperature results for different configuration

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Figure 7

Typical high-pressure turbine blade showing trailing edge cooling openings and pressure-side ejection slots, from Lee (10)

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Figure 8

Typical high-pressure turbine blade showing cross-sectional area and trailing edge detail, from Hill (15)

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Figure 9

Localized heat transfer enhancement on different segments in trailing edge cavities, from Chyu (16)

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Figure 10

Pedestal trailing edge configuration and test results. (a) Transparent view of blade showing pedestal bank at trailing edge. (b) Effect of Reynolds number on performance index (HM/FM) in straight pins with fillets, from Chyu (21).

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Figure 11

Dimensionless flow parameter P as function of ratio of cut-back lip thickness-to-slot for different film cooling effectiveness, from Hill (16)

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Figure 12

Cut-back trailing edge configuration and test results. (a) Schematic showing locations of relevant geometrical parameters. (b) Effect of x∕s and t∕s parameters on trailing edge film effectiveness, from Goldstein (23).



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