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Research Papers

End Wall Loss Reduction of High Lift Low Pressure Turbine Airfoils Using Profile Contouring—Part II: Validation

[+] Author and Article Information
Keith Sangston

Department of Aerospace and
Mechanical Engineering,
University of Arizona,
1130 N Mountain Ave,
Tucson, AZ 85721
e-mail: sangston@email.arizona.edu

Jesse Little

Department of Aerospace and
Mechanical Engineering,
University of Arizona,
1130 N Mountain Ave,
Tucson, AZ 85721
e-mail: jesselittle@email.arizona.edu

M. Eric Lyall

Aerospace Systems Directorate,
Air Force Research Laboratory,
1950 Fifth Street,
Wright Patterson AFB, OH 45433
e-mail: michael.lyall@us.af.mil

Rolf Sondergaard

Aerospace Systems Directorate,
Air Force Research Laboratory,
1950 Fifth Street,
Wright Patterson AFB, OH 45433
e-mail: rolf.sondergaard@us.af.mil

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 23, 2013; final manuscript received September 24, 2013; published online January 31, 2014. Editor: Ronald Bunker.

J. Turbomach 136(8), 081006 (Jan 31, 2014) (10 pages) Paper No: TURBO-13-1196; doi: 10.1115/1.4025952 History: Received August 23, 2013; Revised September 24, 2013

The hypothesis, posed in Part I, that excessive end wall loss of high lift low pressure turbine (LPT) airfoils is due to the influence of high stagger angles on the end wall pressure distribution and not front loading is evaluated in a linear cascade at Re = 100,000 using both experimental and computational studies. A nominally high lift and high stagger angle front-loaded profile (L2F) with aspect ratio 3.5 is contoured at the end wall to reduce the stagger angle while maintaining the front loading. The contouring process effectively generates a fillet at the end wall, so the resulting airfoil is referred to as L2F-EF (end wall fillet). Although referred to as a fillet, this profile contouring process is novel in that it is designed to isolate the effect of stagger angle on end wall loss. Total pressure loss measurements downstream of the blade row indicate that the use of the lower stagger angle at the end wall reduces mixed out mass averaged end wall and passage losses approximately 23% and 10%, respectively. This is in good agreement with computational results used to design the contour which predict 18% and 7% loss reductions. The end wall flow field of the L2F and L2F-EF models is measured using stereoscopic particle image velocimetry (PIV) in the passage. These data are used to quantify changes in the end wall flow field due to the contouring. PIV results show that this loss reduction is characterized by reduced inlet boundary layer separation as well as a change in strength and location of the suction side horseshoe vortex (SHV) and passage vortex (PV). The end wall profile contouring also produces a reduction in all terms of the Reynolds stress tensor consistent with a decrease in deformation work and overall flow unsteadiness. These results confirm that the stagger angle has a significant effect on high-lift front-loaded LPT end wall loss. Low stagger profiling is successful in reducing end wall loss by limiting the development and migration of the low momentum fluid associated with the SHV and PV interaction.

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References

Figures

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Fig. 1

Wind tunnel test section schematic

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Fig. 2

Comparison of L2F and L2F-LS near the end wall

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Fig. 3

CAD model of the fillet modification used to mimic the L2F-EF airfoil design

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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 hot wire and PIV data near OP for L2F. PIV data are acquired at x/Cax = 1.50, while hot wire data are at x/Cax = 1.58 explaining the shift in the vortex system.

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Fig. 6

95% confidence interval as a percentage of local velocity for PIV data at OP

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Fig. 7

In-plane velocity vectors superimposed on out-of-plane vorticity floods for both L2F (left) and L2F-EF (right) at planes 1–4 (top to bottom)

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Fig. 8

Swirling strength for both L2F (left) and L2F-EF (right) at planes 1–4 (top to bottom)

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Fig. 9

Paths of the PV and SHV in the passage for both L2F and L2F-EF

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Fig. 10

TKE for both L2F (left) and L2F-EF (right) at planes 1–4 (top to bottom)

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Fig. 11

In-plane Reynolds stress for both L2F (left) and L2F-EF (right) at planes 1–4 (top to bottom)

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Fig. 12

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

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