Research Papers

Experimental Evaluations of the Relative Contributions to Overall Effectiveness in Turbine Blade Leading Edge Cooling

[+] Author and Article Information
Carol E. Bryant, Connor J. Wiese

Air Force Research Laboratory,
Wright-Patterson Air Force Base, OH 45433

James L. Rutledge

Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433
e-mail: james.rutledge@us.af.mil

Marc D. Polanka

Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 19, 2018; final manuscript received September 27, 2018; published online January 21, 2019. Editor: Kenneth Hall. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Turbomach 141(4), 041007 (Jan 21, 2019) (15 pages) Paper No: TURBO-18-1256; doi: 10.1115/1.4041645 History: Received September 19, 2018; Revised September 27, 2018

Gas turbine components are protected through a combination of internal cooling and external film cooling. Efforts aimed at improving cooling are often focused on either the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. Measurements of overall cooling effectiveness, ϕ, using matched Biot number models allow evaluation of fully cooled components; however, the relative contributions of internal cooling, external cooling, and convection within the film cooling holes are not well understood. Matched Biot number experiments, complemented by computational fluid dynamics (CFD) simulations, were performed on a fully film cooled cylindrical leading edge model to quantify the effects of alterations in the cooling design. The relative influence of film cooling and cooling within the holes was evaluated by selectively disabling individual holes and quantifying how ϕ changed. Testing of several impingement cooling schemes revealed that impingement has a negligible influence on ϕ in the showerhead region. This indicates that the pressure drop penalties with impingement may not always be compensated by an increase in ϕ. Instead, internal cooling from convection within the holes and film cooling were shown to be the dominant contributors to ϕ. Indeed, the numerous holes within the showerhead region impede the ability of internal surface cooling schemes to influence the outside surface temperature. These results may allow improved focus of efforts on the forms of cooling with the greatest potential to improve performance.

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Fig. 2

Coordinate system and hole geometry. Dimensions are shown in cooling hole diameters (dLE = 0.48 cm).

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Fig. 3

Impingement plate designs (A: 49 hole plate, B: 21 offset hole plate, C: 21 inline hole plate, and D: 4 slot plate)

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Fig. 4

Thermocouple locations

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Fig. 5

Baseline overall effectiveness

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Fig. 6

Overall effectiveness with blocked holes at β = 21.5 deg

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Fig. 7

Δϕ with blocked holes at β = 21.5 deg

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Fig. 8

Overall effectiveness with blocked row at x/d = 0

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Fig. 9

Δϕ with blocked row at x/d = 0

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Fig. 10

Δϕ with blocked rows at y/d = 4,8

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Fig. 11

Baseline overall effectiveness from CFD simulations

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Fig. 12

Overall effectiveness at engine design coolant blowing ratios

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Fig. 13

Comparison of overall effectiveness contours with the row at x/d = 0 blocked, M = 0.9

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Fig. 14

Computational fluid dynamics prediction of Δϕ with blocked row at x/d = 0 at engine design blowing ratios

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Fig. 15

Computational fluid dynamics prediction of Δϕ with blocked row at β = 21.5 deg at engine design blowing ratios

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Fig. 16

Computational fluid dynamics prediction of normalized blowing ratio for each row of cooling holes

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Fig. 17

Comparison of overall effectiveness contours with different Biot numbers and the resulting Δϕ

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Fig. 18

Δϕ contours for k = 3.5 W/m/K at M = 0.9 with rows blocked as indicated

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Fig. 19

Sensitivity of ϕ to h/hi for a range of Bi, χ = 0.9

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Fig. 20

Δϕ from impingement plate A

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Fig. 21

Leading edge cross section in yz plane

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Fig. 22

Δϕ from impingement plate B

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Fig. 23

Δϕ from impingement plate C

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Fig. 24

Δϕ from impingement plate D

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Fig. 25

Area-averaged Δϕ for all four impingement plates

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Fig. 26

Coolant warming factors for the impingement plates



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