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Research Papers

Blockage Effects From Simulated Thermal Barrier Coatings for Cylindrical and Shaped Cooling Holes

[+] Author and Article Information
Christopher A. Whitfield

Mechanical and Nuclear Engineering Department,
The Pennsylvania State University,
University Park, PA 16802
e-mail: christopher.whitfield@pw.utc.com

Robert P. Schroeder

Mechanical and Nuclear Engineering Department,
The Pennsylvania State University,
University Park, PA 16802
e-mail: rschroeder@psu.edu

Karen A. Thole

Mechanical and Nuclear Engineering Department,
The Pennsylvania State University,
University Park, PA 16802
e-mail: kthole@engr.psu.edu

Scott D. Lewis

Pratt & Whitney,
400 Main Street,
East Hartford, CT 06118
e-mail: scott.lewis@pw.utc.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 14, 2014; final manuscript received December 1, 2014; published online March 10, 2015. Editor: Ronald Bunker.

J. Turbomach 137(9), 091004 (Sep 01, 2015) (10 pages) Paper No: TURBO-14-1144; doi: 10.1115/1.4029879 History: Received July 14, 2014; Revised December 01, 2014; Online March 10, 2015

Film cooling and sprayed thermal barrier coatings (TBCs) protect gas turbine components from the hot combustion gas temperatures. As gas turbine designers pursue higher turbine inlet temperatures, film cooling and TBCs are critical in protecting the durability of turbomachinery hardware. One obstacle to the synergy of these technologies is that TBC coatings can block cooling holes when applied to the components, causing a decrease in the film cooling flow area thereby reducing coolant flow for a given pressure ratio (PR). In this study, the effect of TBC blockages was simulated on film cooling holes for widely spaced cylindrical and shaped holes. At low blowing ratios for shaped holes, the blockages were found to have very little effect on adiabatic effectiveness. At high blowing ratios, the area-averaged effectiveness of shaped and cylindrical holes decreased as much as 75% from blockage. The decrease in area-averaged effectiveness was found to scale best with the effective momentum flux ratio of the jet exiting the film cooling hole for the shaped holes.

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References

Figures

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Fig. 1

Micrograph of a blocked film cooling hole from Bogard et al. [2]

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Fig. 2

Schematic of wind tunnel used in the current study

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Fig. 3

Cross sections of (a) a blocked cylindrical hole and (b) a blocked shaped hole

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Fig. 4

Axial photographs of the blocked hole exits of (a) a cylindrical hole with a t/D=0.5 blockage, (b) a shaped hole with a t/D=0.5 blockage, and (c) a shaped hole with a t/D=0.9 blockage

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Fig. 5

Discharge coefficients for cylindrical and shaped holes at DR = 1.5

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Fig. 6

Cylindrical hole adiabatic effectiveness contours for DR = 1.5 and M = 0.5: (a) unblocked hole—M = 0.5 and Ieff = 0.18, (b) blocked hole with matched PR—M = 0.26, Ieff = 0.10, and t/D = 0.5, and (c) blocked hole with matched M—M = 0.5, Ieff = 0.44, and t/D = 0.5

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Fig. 7

Cylindrical hole adiabatic effectiveness contours for DR = 1.5 and M = 1: (a) unblocked hole—M = 1.0 and Ieff = 0.70, (b) blocked hole with matched PR—M = 0.63, Ieff = 0.63, and t/D = 0.5, and (c) blocked hole with matched M—M = 1.0, Ieff = 1.66, and t/D = 0.5

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Fig. 8

Cylindrical hole DR = 1.5 laterally averaged effectiveness at (a) M = 0.5, (b) M=0.75, and (c) M=1.0

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Fig. 9

Shaped hole adiabatic effectiveness contours for DR=1.5 and M=0.5 matched M cases: (a) unblocked hole—M = 0.5 and Ieff = 0.03, (b) t/D=0.5 blockage—M = 0.5 and Ieff = 0.05, and (c) t/D=0.9 blockage—M = 0.5 and Ieff = 0.12

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Fig. 10

Shaped hole adiabatic effectiveness contours for DR=1.5 and M=0.5 matched PR cases: (a) unblocked hole—M = 0.5 and Ieff = 0.03, (b) t/D=0.5 blockage—M = 0.44 and Ieff = 0.04, and (c) t/D=0.9 blockage—M = 0.35 and Ieff = 0.06

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Fig. 11

Shaped hole laterally averaged effectiveness for DR=1.5 and M=0.5

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Fig. 12

Shaped hole adiabatic effectiveness contours for DR=1.5 and M=1: (a) unblocked hole—M = 1.0 and Ieff = 0.11, (b) t/D=0.5 blockage, matched PR and M—M = 1.0 and Ieff = 0.2, (c) t/D=0.9, matched PR—M = 0.8 and Ieff = 0.29, and (d) t/D=0.9, matched M—M = 1.0 and Ieff = 0.46

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Fig. 13

Shaped hole laterally averaged effectiveness for DR=1.5 and M=1

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Fig. 14

Shaped hole adiabatic effectiveness contours for DR=1.5 and M=2: (a) unblocked hole—M = 2.0 and Ieff = 0.44, (b) t/D=0.5 blockage, matched PR and M—M = 2.0 and Ieff = 0.84, (c) t/D=0.9 matched PR—M = 1.7 and Ieff = 1.3, and (d) t/D=0.9 matched M—M = 2.0 and Ieff = 1.9

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Fig. 15

Shaped hole laterally averaged effectiveness for DR=1.5 and M=2

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Fig. 16

Area-averaged adiabatic effectiveness at DR=1.5 versus (a) blowing ratio and (b) effective momentum flux ratio. For cylindrical holes, η¯¯ was multiplied by 6.7/6 to account for wider pitchwise spacing.

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Fig. 17

Percent change in area-averaged effectiveness with shaped hole blockage, as a function of the effective momentum flux ratio

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Fig. 18

Percent change in area-averaged effectiveness with cylindrical hole blockage in the current study and in Demling and Bogard [4,14]

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