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Research Papers

Toward the Expansion of Low-Pressure-Turbine Airfoil Design Space

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

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

S. A. Sjolander

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

R. Sondergaard

Air Force Research Laboratory,
WPAFB, OH 45433

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in 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), 061007 (Sep 13, 2013) (8 pages) Paper No: TURBO-11-1046; doi: 10.1115/1.4024796 History: Received March 21, 2011; Revised January 28, 2013

Future engine requirements, including high-altitude flight of unmanned air vehicles as well as an impetus to reduce engine cost and weight, are challenging the current state of the art in low-pressure-turbine airfoil design. These new requirements present low-Reynolds number challenges as well as the need for high-performance, high-lift design concepts. Here, we report on an effort to expand the relatively well established aerodynamic design space for low-pressure turbine airfoils through the application of recent developments in transition modeling to airfoil design. Analytical and experimental midspan performance data and predicted loadings are presented for four high-lift airfoil designs based on the Pack B velocity triangles. The new designs represent a systematic expansion of low-pressure turbine airfoil design space through the application of high-lift design concepts for front- and aft-loaded airfoils. All four designs performed as predicted across a range of operationally representative Reynolds numbers. Full-span loss data for the new high-lift designs reveal increased endwall losses, which, with the application of nonaxisymmetric endwall contouring, have been substantially reduced. Taken holistically, the results presented here demonstrate that accurate transition modeling provides a reliable method to develop optimized, very high-lift airfoil designs. However, further improvements in endwall-loss mitigation technologies are required to enable the implementation of the very high-lift technology presented here in engine systems.

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Figures

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Fig. 1

Low-pressure turbine airfoil counts as a function of pressure ratio demonstrating the trend toward reduced count

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Fig. 2

Four high-lift airfoil designs compared to the baseline Pack B design

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Fig. 3

Design-intent loading distribution for the baseline Pack B airfoil design

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Fig. 4

Pack B loss data from both the CU and WP test facilities. Also plotted are steady loss data for the U1 airfoil design of Howell et al. [5].

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Fig. 5

Pack D-A and D-F surface static-pressure distributions compared with the Pack B loading

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Fig. 6

Comparisons of Pack D-A and D-F measured losses with Pack B included for reference

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Fig. 7

Pack E and F surface pressure distributions with the baseline Pack B shown for reference

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Fig. 8

Pack E and F measured loss data versus Reynolds number with Pack B data included for reference

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Fig. 9

Comparison of loss-versus-Reynolds number characteristics for the four high-lift and baseline Pack B designs with power-law fits for each data set

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Fig. 10

Midspan losses for Pack B, D-A, and D-F designs as a function of the reduced frequency of unsteady bar-generated wake passing

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Fig. 11

Unsteady loss data for Pack B, D-F, and the U1 airfoil design of Howell et al. [5]. The steady losses for Pack B are included for reference.

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Fig. 12

Endwall contouring applied to the Pack D-F design. A single airfoil is shown in this image.

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Fig. 13

Comparisons of the spanwise loss distributions for Pack B and D-F with planar endwalls and Pack D-F with contoured endwalls

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