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Research Papers

Trailing Edge Film Cooling of Gas Turbine Airfoils—External Cooling Performance of Various Internal Pin Fin Configurations

[+] Author and Article Information
T. Horbach, A. Schulz, H.-J. Bauer

Institut für Thermische Strömungsmaschinen (ITS), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany

J. Turbomach 133(4), 041006 (Apr 20, 2011) (9 pages) doi:10.1115/1.4002964 History: Received June 29, 2010; Revised July 01, 2010; Published April 20, 2011; Online April 20, 2011

The present paper describes an experimental study on trailing edge film cooling of modern high pressure turbine blades using coolant ejection through planar slots on a pressure side cutback. The experimental test section consists of a generic scaled-up trailing edge model in an atmospheric open loop wind tunnel, which has been used in several earlier studies. An infrared thermographic measurement technique is employed, which allows for the application of engine-realistic density ratios around 1.6 by increasing the main flow temperature. The effects of different geometric configurations on the structure and performance of the cooling film are investigated in terms of film cooling effectiveness, heat transfer, and discharge behavior. Among other issues, the interaction of internal turbulators, namely, an array of pin fins, with the ejection slot lip is of major interest. Therefore, different designs of the coolant ejection lip are studied. Four different ratios of lip thickness to ejection slot height (t/H=0.2,0.5,1.0,1.5), as well as three different lip profiles representing typical manufacturing imperfections and wear, are investigated. Other geometric variations comprise elliptic pin fins with spanwise and streamwise orientations and the application of land extensions from the internal coolant cavity onto the cutback surface. The blowing ratio is varied at 0.2<M<1.25. In terms of film cooling effectiveness, the results show a strong dependency on ejection lip thickness, and minor improvements are obtained with a rounded ejection lip profile. Significant improvements are achieved using land extensions. The elliptic pin fins have a strong effect on discharge behavior as well as on film cooling effectiveness and heat transfer. Except for the elliptic pin fins, the geometric variations have only a minor influence on heat transfer.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cooling design of a high pressure turbine blade

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Figure 2

Trailing edge test facility

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Figure 3

Generic test section for trailing film cooling experiments with varying ejection lip geometry

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Figure 4

Detailed description of reference geometry (dimensions in mm)

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Figure 5

Geometric variations

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Figure 6

Discharge coefficient versus blowing ratio for geometric variations

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Figure 7

Contours of local adiabatic film cooling effectiveness for the reference geometry at different blowing ratios

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Figure 8

Laterally averaged film cooling effectiveness for the reference geometry (t/H=1; shape A)

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Figure 9

Area-averaged film cooling effectiveness versus blowing ratio for different geometry variations

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Figure 10

Contours of adiabatic film cooling effectiveness for different lip thicknesses at M=0.5

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Figure 11

Contours of normalized heat transfer coefficient for the reference geometry (t/H=1; shape A) at different blowing ratios

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Figure 12

Laterally averaged normalized heat transfer coefficient for the reference geometry (t/H=1; shape A)

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Figure 13

Laterally averaged normalized heat transfer coefficient versus blowing ratio for different lip thicknesses at x/H=2, 6, and 12

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Figure 14

Laterally averaged normalized heat transfer coefficient versus blowing ratio for different lip shapes at x/H=2, 6, and 12

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Figure 15

Laterally averaged normalized heat transfer coefficient versus blowing ratio for the elliptic pin fin configuration at x/H=2, 6, and 12

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