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Research Papers: Heat Transfer Enhancement

Comparisons of Pins/Dimples/Protrusions Cooling Concepts for a Turbine Blade Tip-Wall at High Reynolds Numbers

[+] 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 710072, Shaanxi, Chinaxgn@nwpu.edu.cn

Bengt Sundén1

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

Weihong Zhang

The Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Northwestern Polytechnical University, P.O. Box 552, Xi’an 710072, Shaanxi, China

1

Corresponding author.

J. Heat Transfer 133(6), 061902 (Mar 10, 2011) (9 pages) doi:10.1115/1.4003558 History: Received August 30, 2010; Revised January 29, 2011; Published March 10, 2011; Online March 10, 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 a 180 deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase blade tip lifetime. Pins, 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 180 deg turn and arrays of circular pins, hemispherical dimples, or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are ranging from 100,000 to 600,000. The overall performance of the two-pass channels is evaluated. Numerical results show that the heat transfer enhancement of the pinned-tip is up to a factor of 3.0 higher than that of a smooth tip while the dimpled-tip and protruded-tip provide about 2.0 times higher heat transfer. These augmentations are achieved at the cost of an increase of pressure drop by less than 10%. By comparing the present cooling concepts with pins, dimples, and protrusions, it is shown that the pinned-tip exhibits best performance to improve the blade tip cooling. However, when disregarding the added active area and considering the added mechanical stress, it is suggested that the usage of dimples is more suitable to enhance blade tip cooling, especially at low Reynolds numbers.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Various cooling methods for a turbine blade

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Figure 2

A typical serpentine passage inside a turbine blade

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Figure 3

Heat transfer augmentation devices for a smooth surface

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Figure 4

Schematic diagram of numerical models

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Figure 5

Typical surface grids for computations

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Figure 6

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

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Figure 7

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

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Figure 8

Heat transfer and pressure drop

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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 by thermal performance factor

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Figure 12

Heat transfer coefficient subject to pumping power

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Figure 13

Nusselt number ratio normalized by active area ratio

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Figure 14

Nusselt number ratio normalized by weight ratio

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