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Research Papers

Aerodynamics of a Low-Pressure Turbine Airfoil at Low Reynolds Numbers—Part II: Blade-Wake Interaction

[+] Author and Article Information
Ali Mahallati

Gas Turbine Laboratory,
Institute for Aerospace Research,
National Research Council of Canada,
Ottawa, ON, Canada
e-mail: ali.mahallati@nrc-cnrc.gc.ca

Steen A. Sjolander

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

1Corresponding author.

Manuscript received July 8, 2011; final manuscript received August 4, 2011; published online November 6, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011011 (Nov 06, 2012) (10 pages) Paper No: TURBO-11-1103; doi: 10.1115/1.4006320 History: Received July 08, 2011; Revised August 04, 2011

Part II of this two-part paper presents the aerodynamic behavior of a low-pressure high-lift turbine airfoil, PakB, under the influence of incoming wakes. The periodic unsteady effects of wakes from a single upstream blade-row were measured in a low-speed linear cascade facility at Reynolds numbers of 25,000, 50,000 and 100,000 and at two freestream turbulence intensity levels of 0.4% and 4%. In addition, eight reduced frequencies between 0.53 and 3.2, at three flow coefficients of 0.5, 0.7 and 1.0 were examined. The complex wake-induced transition, flow separation and reattachment on the suction surface boundary layer were determined from an array of closely-spaced surface hot-film sensors. The wake-induced transition caused the separated boundary layer to reattach to the suction surface at all conditions examined. The time-varying profile losses, measured downstream of the cascade, increased with decreasing Reynolds number. The influence of increased freestream turbulence intensity was only evident in between wake-passing events at low reduced frequencies. At higher values of reduced frequency, the losses increased slightly and, for the cases examined here, losses were slightly larger at lower flow coefficients. An optimum wake-passing frequency was observed at which the profile losses were a minimum.

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References

Figures

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Fig. 1

A view of the test section with the wake-generator rig

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Fig. 2

S-T diagrams at Re = 50,000, FSTI = 0.4%, φ = 0.7 and f = 1.52

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Fig. 3

Loss variation at Re = 50,000, FSTI = 0.4%, φ = 0.7 and f = 1.52

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Fig. 4

S-T diagrams at Re = 100,000, FSTI = 0.4%, φ = 0.7 and f = 1.52

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Fig. 5

Normalized mixed-out pressure loss coefficients at FSTI = 0.4%

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Fig. 6

S-T diagrams at Re = 50,000, FSTI = 4%, φ = 0.7 and f = 1.52

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Fig. 7

S-T diagrams at Re = 50,000, FSTI = 0.4%, φ = 0.5 and f = 1.07

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Fig. 8

S-T diagrams at Re = 50,000, FSTI = 0.4%, φ = 0.5 and f = 2.13

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Fig. 9

Normalized mixed-out pressure losses versus reduced frequency

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Fig. 10

S-T diagrams at Re = 50,000, FSTI = 0.4%, φ = 1 and f = 1.07

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