Research Papers

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

[+] Author and Article Information
Andrew C. Chambers

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK

David R. H. Gillespie

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UKdavid.gillespie@eng.ox.ac.uk

Peter T. Ireland

 Rolls-Royce plc., P.O. Box 31, Derby DE24 8BJ, UK

Robert Kingston

 Rolls-Royce plc., P.O. Box 3, Filton, Bristol BS34 7QE, UK

J. Turbomach 132(2), 021001 (Dec 31, 2009) (8 pages) doi:10.1115/1.3140282 History: Received June 09, 2006; Revised March 23, 2009; Published December 31, 2009; Online December 31, 2009

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the buildup of cross flow from upstream jets can be significant and results in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases, a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first four impingement holes, a Nusselt number enhancement of 28–77% was achieved, provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Schematic cross section of a turbine blade

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Figure 2

Impingement channel geometry

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Figure 3

Grid used for CFD analysis of impinging channel

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Figure 4

Flow field for jet aspect ratio=1.0

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Figure 5

Flow field for jet aspect ratio=1.2

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Figure 6

Flow field for jet aspect ratio=1.5

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Figure 7

Flow field for jet aspect ratio=2

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Figure 8

Flow field for jet aspect ratio=1.0,30 deg upstream injection

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Figure 9

Particle lines crossing a measurement plane as a fraction of the total jet particle lines

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Figure 10

Maximum effectiveness on a plane

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Figure 11

Schematic diagram showing the layout of the experimental apparatus

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Figure 12

Details of the elongated hole impingement plate and the hole geometry

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Figure 13

Local Nu̱/Nu¯max, cross flow=5%, Rejet=20,000

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Figure 14

Local jet effectiveness, cross flow=5%, Rejet=20,000

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Figure 15

Nuavg/Nu¯max, Rejet=20,000

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Figure 16

Reduction in effective area caused by separation at impingement holes (view of the y-z plane)

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Figure 17

The effect of Cd on relative jet velocity for the 19 hole impingement channel




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