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Research Papers

Parametric Optimization of Unsteady End Wall Blowing on a Highly Loaded Low-Pressure Turbine

[+] Author and Article Information
Stuart I. Benton

Graduate Fellow
e-mail: benton.53@osu.edu

Chiara Bernardini

Visiting Researcher
e-mail: bernardini.3@osu.edu

Jeffrey P. Bons

Professor
e-mail: bons.2@osu.edu
Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
2300 West Case Road,
Columbus, OH 43235

Rolf Sondergaard

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

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 11, 2013; final manuscript received November 26, 2013; published online January 2, 2014. Editor: Ronald Bunker.

J. Turbomach 136(7), 071013 (Jan 02, 2014) (8 pages) Paper No: TURBO-13-1231; doi: 10.1115/1.4026127 History: Received October 11, 2013; Revised November 26, 2013

Efforts to reduce blade count and avoid boundary layer separation have led to low-pressure turbine airfoils with significant increases in loading as well as front-loaded pressure distributions. These features have been independently shown to increase losses within the secondary flow field at the end wall. Compound angle blowing from discrete jets on the blade suction surface near the end wall has been shown to be effective in reducing these increased losses and enabling the efficient use of highly loaded blade designs. In this study, experiments are performed on the front loaded L2F low-pressure turbine airfoil in a linear cascade. The required mass flow is reduced by decreasing the hole count from previous configurations and from the introduction of unsteady blowing. The effects of pulsing frequency and duty cycle are investigated using phase-locked stereo particle image velocimetry to demonstrate the large scale movement and hysteresis behavior of the passage vortex interacting with the pulsed jets. Total pressure loss contours at the cascade outlet demonstrate that the efficiency benefit is maintained with the use of unsteady forcing.

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References

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Figures

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Fig. 1

Schematic of OSU cascade facility. Measurement planes and stereo-PIV camera setup included. L2F airfoil not shown.

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Fig. 2

Experimental pressure loading for L2F in OSU cascade compared to predictions from both FLUENT and MISES. FLUENT predictions are computed using the case file developed in Lyall et al. [18].

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Fig. 3

Schematic of jet implementation on airfoil suction surface. Jets highlighted in red are used in the optimized four-jet design.

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Fig. 4

Comparison of pitchwise-average total pressure loss coefficient between baseline and seven-jet control configuration for AFRL and OSU facilities. Relative spanwise position of the jets is shown with circles on the left.

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Fig. 5

Comparison of pitchwise-average total pressure loss coefficient for four-jet and seven-jet configurations on the AFRL cascade. Relative spanwise position of the jets is shown on the left, with the four-jet configuration circles filled.

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Fig. 6

Contours of out-of-plane velocity overlaid with in-plane velocity vectors. The vortex center is marked with a black dot. y/S = 0 is the suction surface trailing edge.

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Fig. 7

Vortex location in the PIV plane for steady control as a function of momentum coefficient, comparing the seven-jet and four-jet configurations

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Fig. 8

Normalized total pressure loss in the outlet plane as a function of vortex to suction surface distance for various momentum coefficients

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Fig. 9

Distance between suction surface and vortex center and jet exit velocity as a function of actuation period. Three reduced frequencies are shown, F+= 0.1 (top), F+= 0.4 (middle), and F+= 1.2 (bottom).

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Fig. 10

Hysteresis loops of vortex center in the PIV plane for a range of actuation frequencies

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Fig. 11

Hysteresis loops of the vortex center for variations of duty cycle. All unsteady data are obtained with VR = 5.7.

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Fig. 12

Time-average normalized total pressure loss versus mass flow ratio for various control configurations. Dotted lines connect specific test campaigns, for clarity.

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Fig. 13

Selected phases of the F+= 0.1 actuation cycle demonstrating the initiation (left) and conclusion (right) of the jet actuation

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