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Research Papers

Effect of Blade Profile Contouring on Endwall Flow Structure in a High-Lift Low-Pressure Turbine Cascade

[+] Author and Article Information
Keith Sangston

Department of Aerospace and Mechanical
Engineering, University of Arizona,
Tucson, AZ 85721
e-mail: sangston@email.arizona.edu

Jesse Little

Department of Aerospace and Mechanical
Engineering,
University of Arizona,
Tucson, AZ 85721
e-mail: jesselittle@email.arizona.edu

M. Eric Lyall

Air Force Research Laboratory,
Wright-Patterson AFB, OH 45433
e-mail: michael.lyall.3@us.af.mil

Rolf Sondergaard

Air Force Research Laboratory,
Wright-Patterson AFB, OH 45433
e-mail: rolf.sondergaard@us.af.mil

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 13, 2014; final manuscript received August 15, 2016; published online October 4, 2016. Assoc. Editor: Guillermo Paniagua. This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

J. Turbomach 139(2), 021006 (Oct 04, 2016) (11 pages) Paper No: TURBO-14-1267; doi: 10.1115/1.4034480 History: Received October 13, 2014; Revised August 15, 2016

Previous work has shown that low-stagger contouring near the endwall of a nominally high-lift and high-stagger angle front-loaded low-pressure turbine (LPT) airfoil is successful in reducing endwall loss by limiting the development and migration of low momentum fluid associated with secondary flow structures. The design modification that leads to loss reduction in that study was determined from an intuitive approach based on the premise that reducing flow separation near the endwall will lead to reduced loss production. Those authors also relied heavily upon Reynolds-averaged Navier–Stokes (RANS) based computational tools. Due to uncertainties inherent in computational fluid dynamics (CFD) predictions, there is little confidence that the authors actually achieved true minimum loss. Despite recent advances in computing capability, turbulence modeling remains a shortcoming of modern design tools. As a contribution to overcoming this problem, this paper offers a three-dimensional (3D) view of the developing mean flow, total pressure, and turbulence fields that gave rise to the loss reduction of the airfoil mentioned above. Experiments are conducted in a linear cascade with aspect ratio of 3.5 and Re = 100,000. The results are derived from stereoscopic particle image velocimetry (PIV) and total pressure measurements inside the passage. Overall, the loss reduction correlates strongly with reduced turbulence production. The aim of this paper is to provide readers with a realistic view of mean flow and turbulence development that include all the components of the Reynolds stress tensor to assess, at least qualitatively, the validity of high fidelity computational tools used to calculate turbine flows.

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Figures

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Fig. 1

Comparison of experimental endwall loss, Yew, between LEO and loss correlations

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Fig. 2

Wind tunnel test section schematic

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Fig. 3

Comparison of L2F and L2F-LS near the endwall (top and middle) and CAD model of the blade profile contour modification used to mimic the L2F-EF airfoil design (bottom)

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Fig. 4

(a) Plane locations, orientations, and cascade coordinate system and (b) inset showing rotated coordinate system used for PIV data representation in the passage

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Fig. 5

Comparison of L2F and L2F-EF Y contours (Re = 100,000) (ΔY = 0.05)

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Fig. 6

Total pressure loss contours (lines separated by ΔY = 0.05) superimposed on out-of-plane vorticity for both L2F (left) and L2F-EF (right) at planes 2–4 (top to bottom)

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Fig. 7

Smoke flow visualization illustrating PV roll-up and induced endwall rotation in the downstream section of the cascade passage (plane 4) for the L2F airfoil

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Fig. 8

Total pressure loss contours (lines separated by ΔY = 0.05) superimposed on shear strength for both L2F (left) and L2F-EF (right) at planes 2–4 (top to bottom). PV cores are marked in gray as identified using swirling strength.

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Fig. 9

Total pressure contours (lines separated by ΔY = 0.05) and secondary velocity vectors superimposed on out-of-plane vorticity in the OP for L2F. Key secondary flow features are labeled.

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Fig. 10

Total pressure loss contours (lines separated by ΔY = 0.05) superimposed on TKE for both L2F (left) and L2F-EF (right) at planes 2–4 (top to bottom). PV cores are marked in gray as identified using swirling strength.

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Fig. 11

Comparison of experimental (top) and CFD-predicted (bottom) ∂V′/∂z′ velocity gradient for plane 3

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Fig. 12

Total pressure loss contours (lines separated by ΔY = 0.05) superimposed on total deformation work for both L2F (left) and L2F-EF (right) at planes 2–4 (top to bottom)

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Fig. 13

Example breakdown of the total deformation work field into normal and shear components (L2F-EF, plane 4)

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Fig. 14

Deformation work breakdown by plane. Area average net percent contribution of shear and normal terms.

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Fig. 15

Breakdown of the deformation work tensor into area average net percent contribution to the total deformation work (plane 4)

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