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Research Papers

Estimating the Loss Associated With Film Cooling for a Turbine Stage

[+] Author and Article Information
Chia Hui Lim

Whittle Laboratory, Department of Engineering, University of Cambridge, Cambridge CB3 0DY, UKchl44@cam.ac.uk

Graham Pullan

Whittle Laboratory, Department of Engineering, University of Cambridge, Cambridge CB3 0DY, UKgp10006@cam.ac.uk

John Northall

 Rolls-Royce plc, P.O. Box 31, Derby DE24 8BJ, UKjohn.northall@rolls-royce.com

J. Turbomach 134(2), 021011 (Jun 27, 2011) (10 pages) doi:10.1115/1.4003255 History: Received October 04, 2010; Revised October 26, 2010; Published June 27, 2011; Online June 27, 2011

A methodology is presented to allow designers to estimate the penalty for turbine efficiency associated with film cooling. The approach is based on the control volume analysis of Hartsel and the entropy-based formulations of Young and Wilcock. The present work extends these techniques to include flow ejected at compound angles and uses three-dimensional computational fluid dynamics (CFD) to provide the mainstream flow properties. The method allows the loss contribution from each hole to be identified separately. The proposed method is applied to an aeroengine high-pressure turbine stage. It is found that, if the efficiency definition includes all irreversibilities, the penalty associated with film cooling would be 8.0%. However, if the pragmatic approach is adopted whereby the unavoidable entropy generated due to the equilibration of coolant and mainstream static temperatures is ignored, the efficiency penalty is 0.7%. Finally, a series of case studies is used to quantify the impact of changes to the local mainstream flow direction and coolant ejection angle on the predicted turbine efficiency. It is shown, quantitatively, that reducing the angle between the directions of the coolant and mainstream flows offers the greatest potential for the designer to improve film-cooled turbine efficiency.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Definitions of mainstream and coolant mixture states, after Young and Horlock (9)

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Figure 2

Contours of κ as a function of α and β

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Figure 3

Three cooling holes with different α and β, but with the same κ=45 deg

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Figure 4

Contours of ζmix,KEloc as a function of κ and velocity ratio Vc/Vg

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Figure 5

NGV; baseline case: mainstream and coolant flow unit vectors

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Figure 6

NGV; baseline case: cooling hole ζmix,KEblade and contours of Mg(Δ contours=0.1)

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Figure 7

NGV; baseline case: cooling hole normalized mc and contours of Mg(Δ contours=0.1)

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Figure 8

NGV; baseline case: cooling hole angle κ and contours of Mg(Δ contours=0.1)

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Figure 9

NGV; baseline case and Case Studies 1 and 2: cumulative ζmix,KErow from LE to TE

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Figure 10

NGV; baseline case: cooling hole ζmix,Qblade and contours of Tg/T01¯(Δ contours=0.1)

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Figure 11

Rotor; baseline case: mainstream and coolant flow unit vectors

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Figure 12

Rotor; baseline case: cooling hole ζmix,KEblade and contours of Mgrel(Δ contours=0.1)

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Figure 13

Rotor; baseline case: cooling hole normalized mc and contours of Mgrel(Δ contours=0.1)

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Figure 14

Rotor; baseline case: cooling hole angle κ and contours of Mgrel(Δ contours=0.1)

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Figure 15

Rotor; baseline case and Case Studies 1 and 2: cumulative ζmix,KErow from LE to TE

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Figure 16

Rotor; baseline case: cooling hole ζmix,Qblade and contours of Tg/T01¯(Δ contours=0.1)

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Figure 17

Rotor; Case Study 1: cooling hole angle κ and contours of Mgrel(Δ contours=0.1)

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Figure 18

Rotor suction surface limiting streamlines for the baseline case and Case Study 2

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Figure 19

Rotor; Case Study 2: cooling hole angle κ and contours of Mgrel(Δ contours=0.1)

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Figure 20

Rotor; baseline case and Case Study 3: cumulative ζmix,KErow from LE to TE

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Figure 21

Control volume for “Hartsel” constant static pressure mixing

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Figure 23

Case 2—ejection of coolant at a compound angle (β≠0 deg)

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Figure 22

Case 1—ejection of coolant in the streamwise direction (β=0 deg)

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