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Research Papers

Predictions of Enhanced Heat Transfer of an Internal Blade Tip-Wall With Hemispherical Dimples or Protrusions

[+] Author and Article Information
Gongnan Xie

The Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Northwestern Polytechnical University, P.O. Box 552, Xi’an, Shaanxi 710072, China; Department of Energy Sciences, Division of Heat Transfer, Lund University, P.O. Box 118, SE-22100 Lund, Sweden

Bengt Sundén1

Department of Energy Sciences, Division of Heat Transfer, Lund University, P.O. Box 118, SE-22100 Lund, Swedenbengt.sunden@energy.lth.se

Qiuwang Wang

State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China

1

Corresponding author.

J. Turbomach 133(4), 041005 (Apr 19, 2011) (9 pages) doi:10.1115/1.4002963 History: Received June 29, 2010; Revised July 02, 2010; Published April 19, 2011; Online April 19, 2011

The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with 180 deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. Dimples and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with a 180 deg turn and arrays of hemispherical dimples or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are in the range of 100,000–600,000. The computations are three dimensional, steady, incompressible, and nonrotating. The overall performance of the two-pass channels is also evaluated. It is found that due to the combination of turning impingement and protrusion crossflow or dimple advection, the heat transfer coefficient of the augmented tip is a factor of 2.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a penalty of pressure drop by around 5%. By comparing the present dimples’ or protrusions’ performance with others in previous works, it is found that the augmented tips show the best performance, and the dimpled or protruded tips are superior to those pin-finned tips when the active area enhancement is excluded. It is suggested that dimples and protrusions can be used to enhance blade tip heat transfer and hence improve blade tip cooling.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 12

Performance comparison of two tips by criterion II

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Figure 13

Performance comparison of dimples for augmenting straight channels or two-pass channels

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Figure 14

Nusselt number ratio normalized by active area ratio

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Figure 1

A typical serpentine passage inside a turbine blade

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Figure 2

Schematic diagram of numerical models

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Figure 3

Typical cross-section grids for computations

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Figure 4

Flow fields in the center of turn, Re=200,000

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Figure 5

Distributions of spanwise x-velocity, Re=200,000

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Figure 6

Temperature contours of tip-wall, Re=200,000

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Figure 7

Sectional temperature contours, Re=200,000

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Figure 8

Heat transfer and pressure drop of two channels

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Figure 9

Normalized Nusselt number and friction factor

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Figure 10

Typical profiles of local heat transfer enhancement

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Figure 11

Performance comparison of three tips by criterion I

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