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Research Papers

The Augmentation of Internal Blade Tip-Cap Cooling by Arrays of Shaped Pins

[+] Author and Article Information
Ronald S. Bunker

 GE Global Research Center, Niskayuna, NY 12309

J. Turbomach 130(4), 041007 (Jul 31, 2008) (8 pages) doi:10.1115/1.2812333 History: Received June 06, 2007; Revised June 23, 2007; Published July 31, 2008

The objective of the present study is to demonstrate a method to provide substantially increased convective heat flux on the internal cooled tip cap of a turbine blade. The new tip-cap augmentation consists of several variations involving the fabrication or placement of arrays of discrete shaped pins on the internal tip-cap surface. Due to the nature of flow in a 180deg turn, the augmentation mechanism and geometry have been designed to accommodate a mixture of impingementlike flow, channel flow, and strong secondary flows. A large-scale model of a sharp 180deg tip turn is used with the liquid crystal thermography method to obtain detailed heat transfer distributions over the internal tip-cap surface. Inlet channel Reynolds numbers range from 200,000 to 450,000 in this study. The inlet and exit passages have aspect ratios of 2:1, while the tip turn divider-to-cap distance maintains nearly the same hydraulic diameter as the passages. Five tip-cap surfaces were tested including a smooth surface, two different heights of aluminum pin arrays, one more closely spaced pin array, and one pin array made of insulating material. Effective heat transfer coefficients based on the original smooth surface area were increased by up to a factor of 2.5. Most of this increase is due to the added surface area of the pin array. However, factoring this surface area effect out shows that the heat transfer coefficient has also been increased by about 20–30%, primarily over the base region of the tip cap itself. This augmentation method resulted in negligible increase in tip turn pressure drop over that of a smooth surface.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

General layout of test model

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Figure 2

Assembly view of test model

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Figure 3

Instrumentation locations

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Figure 4

Aluminum pin array test surface

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Figure 5

Aluminum base fillets with insulator pins

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Figure 6

Short aluminum pin array

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Figure 8

Smooth tip turn Nu distributions for Re of 200,000, 310,000, and 440,000

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Figure 9

Smooth surface tip heat transfer augmentation relative to fully developed, turbulent duct flow for Re of 200,000, 310,000, and 440,000

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Figure 18

Test model pressure distribution comparisons

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Figure 17

Effect of pin array turbulation ability on heat transfer augmentation

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Figure 16

Tip surface average Nu for all tests

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Figure 15

Comparison of five tip turn surfaces at Re of 440,000

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Figure 14

Nu distributions for dense, shorter aluminum pin array for Re of 200,000, 310,000, and 440,000

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Figure 13

Tall aluminum pin array surface tip heat transfer augmentation relative to smooth surface for Re of 200,000, 310,000, and 440,000

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Figure 12

Tall aluminum pin array Nu distributions for Re of 200,000, 310,000, and 440,000

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Figure 11

Tall insulating pin array surface tip heat transfer augmentation relative to smooth surface for Re of 200,000, 310,000, and 440,000

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Figure 10

Nu distributions for insulating pin array for Re of 200,000, 310,000, and 440,000

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