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Research Papers

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

[+] 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 4, 2015; final manuscript received November 17, 2015; published online January 5, 2016. Editor: Kenneth C. Hall.

J. Turbomach 138(4), 041008 (Jan 05, 2016) (10 pages) Paper No: TURBO-15-1245; doi: 10.1115/1.4032165 History: Received November 04, 2015; Revised November 17, 2015

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter (LDV). Friction coefficients obtained with the oil film interferometry (OFI) method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

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Figures

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Fig. 1

Depiction of (a) the low-speed wind tunnel with corner test section and (b) the test section with inlet boundary layer measurement locations indicated

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Fig. 2

(a) Isometric view of the contoured endwall, (b) flowfield measurement plane with local coordinate system indicated, and (c) passage boundary layer measurement locations with local velocity transformations indicated

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Fig. 3

(a) Schematic of oil film development due to shear and (b) sample interferogram which demonstrates friction coefficient directionality

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Fig. 4

(a) Measurements and predictions of streamwise velocity at midspan for plane A and (b) measurements and predictions of flow angles at midspan

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Fig. 5

(a) Endwall oil flow visualization of Lynch et al. [18] for the (a) flat and (b) contoured endwalls, overlaid with the measurement locations in this study

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Fig. 6

Contours of mean streamwise velocity and mean secondary velocity vectors at plane A (see Fig. 2) for the (a) flat and (b) contoured endwalls

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Fig. 7

Contours of TKE normalized by inlet velocity magnitude at plane A for the (a) flat and (b) contoured endwalls

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Fig. 8

Contours of TKE normalized by the local velocity magnitude at plane A for the (a) flat and (b) contoured endwalls

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Fig. 9

Boundary layer profiles of mean streamwise velocity in plane A for the flat and contoured endwalls

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Fig. 10

Boundary layer profiles of mean cross-stream velocity in plane A for the flat and contoured endwalls

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Fig. 11

Boundary layer profiles of mean flow angle relative to the freestream angle in plane A, for the flat and contoured endwalls. The results below z/δ = 0.01 are wall shear angles from the friction coefficient measurements.

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Fig. 12

Measured endwall heat transfer and friction coefficients at plane A, where the velocity scale for St and Cf is the local freestream velocity

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