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TECHNICAL PAPERS

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: Low-Speed Investigation

[+] Author and Article Information
Xue Feng Zhang1

Whittle Laboratory,  University of Cambridge, Madingley Road, Cambridge CB3 0DY, UKgeorge.zhang@pwc.ca

Maria Vera, Howard Hodson

Whittle Laboratory,  University of Cambridge, Madingley Road, Cambridge CB3 0DY, UK

Neil Harvey

 Compression Systems, Rolls-Royce plc, Mail Code PCF-2, P.O. Box 31, Derby DE24 8BJ, UK

1

Current address: Turbine Aerodynamics, Pratt & Whitney, Canada.

J. Turbomach 128(3), 517-527 (Feb 01, 2005) (11 pages) doi:10.1115/1.2187524 History: Received October 01, 2004; Revised February 01, 2005

An experimental study was conducted to improve the performance of an aft-loaded ultra-high-lift low-pressure turbine blade known as U2 at low Reynolds numbers. This was achieved by manipulation of the laminar-turbulent transition process on the suction surface. The U2 profile was designed to meet the targets of reduced cost, weight and fuel burn of aircraft engines. The studies were conducted on both low-speed and high-speed experimental facilities under the unsteady flow conditions with upstream passing wakes. The current paper presents the low-speed investigation results. On the smooth suction surface, the incoming wakes are not strong enough to suppress the separation bubble due to the strong adverse pressure gradient on the suction surface and the low wake passing frequency, which allows the separation between the wakes more time to re-establish. Therefore, the profile losses of this ultra-high-lift blade are not as low as conventional or high-lift blades at low Reynolds numbers even in unsteady flows. Two different types of passive separation control devices, i.e., surface trips and air jets, were investigated to further improve the blade performance. The measurement results show that the profile losses can be further reduced to the levels similar to those of the high-lift and conventional blades due to the aft-loaded nature of this ultra-high-lift blade. Detailed surveys of the blade surface boundary layer developments showed that the loss reduction was due to the suppression of the separation underneath the wakes, the effect of the strengthened calmed region and the smaller separation bubble between wakes.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of U2 cascade with moving bars

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Figure 2

Schematic of flow control methods; (a) positive step, (b) negative step, (c) distributed roughness, (d) round dimple, (e) long dimple, (f) vented air jet

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Figure 3

Surface velocity distributions at Tu=0.5%

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Figure 4

Total pressure loss coefficients on smooth surface, Tu=0.5%

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Figure 5

Raw velocity traces at Yn=0.2mm on smooth surface, Re=130,000, Tu=0.5%

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Figure 6

Normalized velocity profiles on smooth surface at Re=130,000, Tu=0.5%

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Figure 7

Shape factor H12 (solid contour) and intermittency (contour lines) on smooth surface at Re=130,000, Tu=0.5%

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Figure 8

Total pressure loss coefficients with positive rectangular steps SS26 and SS17

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Figure 9

Raw velocity traces at Yn=0.2mm with surface trip SS26 at Re=130,000, Tu=0.5%

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Figure 10

Normalized velocity profiles with surface trip SS26 at Re=130,000, Tu=0.5%

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Figure 11

Shape factor H12 (solid contour) and intermittency (contour lines) with surface trip SS26 at Re=130,000, Tu=0.5%

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Figure 12

Trailing edge momentum thickness with∕ without surface trip SS26 at Re=130,000, Tu=0.5%

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Figure 13

Momentum thickness at selected locations with∕without surface trip SS26 at Re=130,000, Tu=0.5%

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Figure 14

Total pressure loss coefficients with different surface trips at Tu=0.5% in unsteady flow

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Figure 15

Total pressure loss coefficients with air jets at Tu=0.5% in unsteady flow

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Figure 16

Trailing edge momentum thickness on vented blade at Re=130,000, Tu=0.5%

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Figure 17

Total pressure loss coefficients at high speed (M=0.65) in unsteady flow

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