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Research Papers

Experimental Investigation Into Unsteady Effects on Film Cooling

[+] Author and Article Information
Richard J. Fawcett

Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdomrichard.fawcett@eng.ox.ac.uk

Andrew P. S. Wheeler

School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom

Li He

Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom

Rupert Taylor

 Rolls-Royce, Turbine Systems, Bristol BS34 7QE, United Kingdom

J. Turbomach 134(2), 021015 (Jun 28, 2011) (9 pages) doi:10.1115/1.4003053 History: Received June 28, 2010; Revised July 23, 2010; Published June 28, 2011; Online June 28, 2011

The benefits of different film cooling geometries are typically assessed in terms of their time-averaged performance. It is known that the mixing between the coolant film and the main turbine passage flow is an unsteady process. The current study investigates the forms of unsteadiness that occur in engine-representative film cooling flows and how this unsteadiness affects the mixing with the mainstream flow. Cylindrical and fan-shaped cooling holes across a range of hole blowing ratios have been studied experimentally using particle image velocimetry and high speed photography. Coherent unsteadiness is found in the shear layer between the jet and the mainstream for both cylindrical and fan-shaped cooling holes. Its occurrence and sense of rotation is found to be controlled by the velocity difference between the mainstream flow and the jet, which is largely determined by the blowing ratio.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Plan view of oxford super scale cascade

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Figure 2

Blade pressure surface Cp profile at 50% and 10% span compared with Palafox (16)

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Figure 3

Boundary layer profile at 50% axial chord and 50% span with no cooling holes

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Figure 4

Cooling hole geometries: (top) interchangeable module with cutting planes used to show hole dimensions, (lower left) cylindrical hole dimensions, and (lower right) fan-shaped hole dimensions

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Figure 5

Variation in the hole discharge coefficient (CD) with blowing ratio for the cylindrical and fan-shaped holes

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Figure 6

The spanwise and secondary flow measurement planes

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Figure 7

(Left) Mean velocity and (right) rms velocity in the spanwise plane at blade midspan for a cylindrical hole with increasing blowing ratio

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Figure 8

(Left) Mean pixel intensity and (right) variance in the spanwise plane at blade midspan for a cylindrical hole with increasing blowing ratio. Recorded at 2000 Hz.

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Figure 9

(Left) Mean pixel intensity and (right) variance in the secondary flow plane 2D downstream of the hole exit centre for a cylindrical hole with increasing blowing ratio. Recorded at 1000 Hz.

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Figure 10

Normalized mean vorticity in secondary flow plane 2D and 4D downstream of hole exit center for a cylindrical hole for M=1.4

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Figure 11

Instantaneous images of the jet (left) in the spanwise plane and (right) in the secondary flow plane 2D downstream with increasing blowing ratio for a cylindrical hole

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Figure 12

(Left) Mean pixel intensity and (right) variance in the spanwise plane 0.5D below blade midspan for a fan-shaped hole with increasing blowing ratio. Recorded at 1000 Hz.

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Figure 13

(Left) Mean pixel intensity and (right) variance in the secondary flow plane 1D downstream of the hole exit center for a fan-shaped hole with increasing blowing ratio. Recorded at 1000 Hz.

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Figure 14

Normalized mean vorticity in secondary flow plane 2D downstream of hole exit center for a fan-shaped hole of M=1.0 and 1.9.

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Figure 15

Images of the jet (left) in the spanwise plane and (right) in the secondary flow plane 1d downstream with increasing blowing ratio for a fan-shaped hole

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Figure 16

Variation in pixel intensity with time for a typical point in the shear layer and the corresponding Fourier spectra in the jet from the cylindrical hole when M=2.0

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Figure 17

Strouhal number for the coherent shear layer vortices in the jet from the cylindrical hole of M=2.0 and fan-shaped hole of M=1.4

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Figure 18

Schematic to show the observed trends in unsteadiness in the current experiment

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