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Research Papers

Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage

[+] Author and Article Information
Stephen P. Lynch

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

Karen A. Thole

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

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 18, 2015; final manuscript received October 18, 2016; published online January 24, 2017. Editor: Kenneth Hall.

J. Turbomach 139(5), 051002 (Jan 24, 2017) (10 pages) Paper No: TURBO-15-1268; doi: 10.1115/1.4035202 History: Received November 18, 2015; Revised October 18, 2016

Turbine blade components in an engine are typically designed with gaps between parts due to manufacturing, assembly, and operational considerations. Coolant is provided to these gaps to limit the ingestion of hot combustion gases. The interaction of the gaps, their leakage flows, and the complex vortical flow at the endwall of a turbine blade can significantly impact endwall heat transfer coefficients and the effectiveness of the leakage flow in providing localized cooling. In particular, a platform gap through the passage, representing the mating interface between adjacent blades in a wheel, has been shown to have a significant effect. Other important turbine blade features present in the engine environment are nonaxisymmetric contouring of the endwall, and an upstream rim seal with a gaspath cavity, which can reduce and increase endwall vortical flow, respectively. To understand the platform gap leakage effect in this environment, measurements of endwall heat transfer, and film cooling effectiveness were performed in a scaled blade cascade with a nonaxisymmetric contour in the passage. A rim seal with a cavity, representing the overlap interface between a stator and rotor, was included upstream of the blades and a nominal purge flowrate of 0.75% of the mainstream was supplied to the rim seal. The results indicated that the endwall heat transfer coefficients increased as the platform gap net leakage increased from 0% to 0.6% of the mainstream flowrate, but net heat flux to the endwall was reduced due to high cooling effectiveness of the leakage flow.

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Figures

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Fig. 1

Depiction of the low-speed wind tunnel and large-scale test section

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Fig. 2

Depiction of the rim cavity, rim seal leakage geometry, and platform gap leakage geometry

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Fig. 3

Depictions of the (a) nonaxisymmetric endwall contour with platform gap and (b) cross section view of gap

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Fig. 4

Estimated platform gap leakage velocities along the gap length for the net leakage flowrates

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Fig. 5

Endwall film cooling geometry, with injection directions indicated

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Fig. 6

Comparison of (a) oil flow visualization, (b) endwall heat transfer, and (c) film cooling effectiveness for the nominal case of 0.75% MFR rim seal flow and 0.3% MFR platform gap flow

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Fig. 7

Endwall heat transfer contours for 0.75% MFR rim seal leakage with net platform gap MFR of (a) 0%, (b) 0.3%, and (c) 0.6%

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Fig. 8

Endwall heat transfer for varying platform gap MFR, extracted along an inviscid streamline path passing through the center of the passage

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Fig. 9

Heat transfer augmentation with the net gap flow relative to heat transfer with 0% net gap flow, for gap MFR's of (a) 0.3% and (b) 0.6%

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Fig. 10

Film cooling effectiveness for 0.75% MFR rim seal leakage with net gap MFR of (a) 0%, (b) 0.3%, and (c) 0.6%

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Fig. 11

Endwall film cooling effectiveness for varying gap MFR, plotted along an inviscid streamline through the center of the passage

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Fig. 12

Net heat flux reduction with the addition of gap leakage flow for (a) 0.3% gap MFR and (b) 0.6% gap MFR

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Fig. 13

Percent increase in area-averaged endwall heat transfer and film cooling, and resulting area-averaged NHFR, for increasing platform gap flow relative to 0% gap MFR

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