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Technical Briefs

Experimental Study of Heat Transfer Augmentation Near the Entrance to a Film Cooling Hole in a Turbine Blade Cooling Passage

[+] Author and Article Information
Gerard Scheepers

Department of Mechanical Engineering, University of Pretoria, Pretoria 0002, South Africagerard@qfin.net

R. M. Morris

Department of Mechanical Engineering, University of Pretoria, Pretoria 0002, South Africa

J. Turbomach 131(4), 044501 (Jun 30, 2009) (11 pages) doi:10.1115/1.3066294 History: Received December 07, 2007; Revised August 31, 2008; Published June 30, 2009

Film cooling is extensively used by modern gas turbine blade designers as a means of limiting the blade temperature when exposed to extreme combustor outlet temperatures. The following paper describes an experimental study of heat transfer near the entrance to a film cooling hole in a turbine blade cooling passage. Steady state heat transfer results were acquired by using a transient measurement technique in a 40 times actual rectangular channel, representative of an internal cooling channel of a turbine blade. Platinum thin film gauges were used to measure the inner surface heat transfer augmentation as a result of thermal boundary layer renewal and impingement near the entrance of a film cooling hole. Measurements were taken at various suction ratios, extraction angles, and wall temperature ratios with a main duct Reynolds number of 25,000. A numerical technique based on the resolution of the unsteady conduction equation, using a Crank–Nicholson scheme, is used to obtain the surface heat flux from the measured surface temperature history. Computational fluid dynamics predictions were also made to provide better understanding of the near-hole flow. The results show extensive heat transfer enhancement as a function of extraction angle and suction ratio in the near-hole region and demonstrate good agreement with a corresponding study. Furthermore it was shown that the effect of a wall-to-coolant ratio is of a second order and can therefore be considered negligible compared with the primary variables such as the suction ratio and extraction angle.o

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic layout of the experimental setup

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Figure 2

Schematic cut-away of the experimental channel

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Figure 3

Numerical domain with boundary conditions

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Figure 4

Near-hole mesh configuration

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Figure 5

Line averages downstream of the extraction hole

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Figure 6

Line averages downstream of the 90 deg extraction hole

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Figure 7

Line averages downstream of the 150 deg extraction hole

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Figure 8

Velocity vectors near the entrance to the 90 deg extraction hole at SR=2.5 (encircled area indicates coolant impingement)

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Figure 9

Velocity vectors near the entrance to the 90 deg extraction hole at SR=5 (encircled area indicates coolant impingement)

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Figure 10

Velocity vectors near the entrance to the 150 deg extraction hole at SR=2.5 (encircled area indicates coolant impingement)

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Figure 11

Velocity vectors near the entrance to the 150 deg extraction hole at SR=5 (encircled area indicates coolant impingement)

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Figure 12

Line averages downstream of the 90 deg extraction hole

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Figure 13

Line averages downstream of different angled extraction holes

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Figure 14

Line averages downstream of different angled extraction holes

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Figure 15

Line averages downstream of the 150 deg extraction hole

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Figure 16

Average heat transfer enhancement downstream of the 90 deg and 150 deg extraction holes at various SR ratios

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Figure 17

Average heat transfer enhancement downstream of the 90 deg extraction hole at different Tw/Tc ratios

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