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Research Papers

Application of Nonaxisymmetric Endwall Contouring to Conventional and High-Lift Turbine Airfoils

[+] Author and Article Information
E. A. Grover

Aerodynamics Group,
United Technologies,
Pratt & Whitney,
East Hartford, CT 06108

S. A. Sjolander

Department of Mechanical and
Aerospace Engineering,
Carleton University,
Ottawa, ON, K1S 5B6, Canada

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received March 21, 2011; final manuscript received January 28, 2013; published online September 13, 2013. Editor: David Wisler.

J. Turbomach 135(6), 061006 (Sep 13, 2013) (8 pages) Paper No: TURBO-11-1045; doi: 10.1115/1.4024023 History: Received March 21, 2011; Revised January 28, 2013

Here, we report on the application of nonaxisymmetric endwall contouring to mitigate the endwall losses of one conventional and two high-lift low-pressure turbine airfoil designs. The design methodology presented combines a gradient-based optimization algorithm with a three-dimensional computational fluid dynamics (CFD) flow solver to systematically vary a free-form parameterization of the endwall. The ability of the CFD solver employed in this work to predict endwall loss modifications resulting from nonaxisymmetric contouring is demonstrated with previously published data. Based on the validated trend accuracy of the solver for predicting the effects of endwall contouring, the magnitude of predicted viscous losses forms the objective function for the endwall design methodology. This system has subsequently been employed to optimize contours for the conventional-lift Pack B and high-lift Pack D-F and Pack D-A low-pressure turbine airfoil designs. Comparisons between the predicted and measured loss benefits associated with the contouring for Pack D-F design are shown to be in reasonable agreement. Additionally, the predictions and data demonstrate that the Pack D-F endwall contour is effective at reducing losses primarily associated with the passage vortex. However, some deficiencies in predictive capabilities demonstrated here highlight the need for a better understanding of the physics of endwall loss-generation and improved predictive capabilities.

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Figures

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Fig. 1

Prototypical endwall flow topology in a row of turbine airfoils. Inlet boundary layer velocity vectors are shown in yellow, while the passage vortex is marked both by streamlines and by an isosurface of TKE (see online version for color).

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Fig. 2

Comparisons of the Pack B and high-lift Pack D airfoil designs. The Pack D designs generate 25% more lift per airfoil than the Pack B design.

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Fig. 3

Loading distributions for the Pack B, D-A, and D-F airfoil designs (data from Popovic and Sjolander [22])

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Fig. 4

Comparisons of span-wise loss characteristics for the Pack B and high-lift Pack D airfoil designs (data is from Zoric and Sjolander [26])

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Fig. 5

Comparisons of predicted and measured span-wise loss characteristics for the Pack B and high-lift Pack D airfoil designs

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Fig. 6

Comparisons of predicted and measured exit-plane loss distributions for the Langston cascade with and without contouring. Data is from Becz and Langston [34].

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Fig. 7

Example distribution of control points applied to a low-pressure turbine airfoil

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Fig. 8

Optimized endwall shapes for Pack B, D-A, and D-F airfoils

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Fig. 9

Root-section loadings for the Pack B and high-lift Pack D-F airfoil designs with and without endwall contouring

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Fig. 10

Predicted results displaying exit-plane total pressure loss distributions as well as the passage vortex marked by an isosurface of TKE. The same TKE level is used in both the flat and contoured realizations.

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Fig. 11

Pack D-F exit-plane total pressure loss distributions from, at top, experimentation and predictions below. Axial location is 1.4Cx downstream of leading edge.

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Fig. 12

Measured and predicted mass-averaged span-wise loss distributions for Pack D-F with flat and contoured endwalls

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