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Research Papers

Separation Control on a Very High Lift Low Pressure Turbine Airfoil Using Pulsed Vortex Generator Jets

[+] Author and Article Information
Ralph J. Volino

Department of Mechanical Engineering, United States Naval Academy, Annapolis, MD 21402-5042volino@usna.edu

Olga Kartuzova

Department of Mechanical Engineering, Cleveland State University, Cleveland, OH 44115-2425kartuzova_olga@hotmail.com

Mounir B. Ibrahim

Department of Mechanical Engineering, Cleveland State University, Cleveland, OH 44115-2425m.ibrahim@csuohio.edu

J. Turbomach 133(4), 041021 (Apr 25, 2011) (13 pages) doi:10.1115/1.4003024 History: Received June 29, 2010; Revised July 11, 2010; Published April 25, 2011; Online April 25, 2011

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. Computational results from a large eddy simulation of one case showed reattachment in agreement with the experiment. In cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift and a reduction in total pressure losses. Phase averaged velocity profiles and wavelet spectra of the velocity show the VGJ disturbance causes the boundary layer to reattach, but that it can reseparate between disturbances. When the disturbances occur at high enough frequency, the time available for separation is reduced, and the separation bubble remains closed at all times.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Drawings of test section: (a) linear cascade and (b) airfoil with VGJ holes and cross section of hole geometry

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Figure 2

Cp profiles for steady blowing, Re=25,000 cases

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Figure 3

Pressure results for F=0.14, Re=25,000 cases: (a) Cp and (b) total pressure loss

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Figure 4

Pressure results for F=0.28, Re=25,000 cases: (a) Cp and (b) total pressure loss

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Figure 5

Cp profiles for F=0.56, Re=25,000 cases

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Figure 6

Cp profiles for F=1.12, Re=25,000 cases

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Figure 7

Total pressure loss profiles for F=0.56 and F=1.12, Re=25,000 cases

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Figure 8

Integrated pressure results for Re=25,000 cases: (a) ratio of lift to lift in inviscid case, (b) total pressure loss, and (c) change in exit flow angle from high Re case

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Figure 9

Time averaged velocity profiles at six streamwise stations for Re=25,000 cases with no jets and jets with D=10%: (top) mean velocity and (bottom) rms velocity

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Figure 10

Phase averaged mean velocity profiles for Re=25,000 cases, columns for six streamwise stations, rows for phases in pulsing cycle: black (blue)—F=0.28, D=10%, B=2.0; gray (red)—F=0.56, D=10%, B=2.0

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Figure 11

Wavelet spectra computed at y locations of maximum u′ in time averaged profiles and shown as function of time and frequency at six streamwise stations, F=0.28, D=10%, B=2.0, Re=25,000, solid white line is leading edge of disturbance, dashed white line is trailing edge

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Figure 12

Wavelet spectra as function of distance from wall and frequency at stations 2–6 (columns) and various phases (rows), F=0.28, D=10%, B=2.0, Re=25,000

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Figure 13

Wavelet spectra computed at y locations of maximum u′ in time averaged profiles and shown as function of time and frequency at six streamwise stations, F=0.56, D=10%, B=2.0, Re=25,000, solid white line is leading edge of disturbance, dashed white line is trailing edge

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Figure 14

Cp profiles for steady blowing, Re=50,000 cases

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Figure 15

Pressure results for F=0.14, Re=50,000 cases: (a) Cp and (b) total pressure loss

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Figure 16

Pressure results for F=0.28, Re=50,000 cases: (a) Cp and (b) total pressure loss

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Figure 17

Pressure results for F=0.56, Re=50,000 cases: (a) Cp and (b) total pressure loss

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Figure 18

Integrated pressure results for Re=50,000 cases: (a) ratio of lift to lift in inviscid case, (b) total pressure loss, and (c) change in exit flow angle from high Re case

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Figure 19

Time averaged velocity profiles at six streamwise stations for Re=50,000 cases with no jets and jets with D=10%: (top) mean velocity and (bottom) rms velocity

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Figure 20

Phase averaged mean velocity profiles for Re=50,000 cases, columns for six streamwise stations, rows for phases in pulsing cycle: black (blue)—F=0.28, D=10%, B=1.0; gray (red)—F=0.56, D=10%, B=0.75

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Figure 21

Wavelet spectra computed at y locations of maximum u′ in time averaged profiles and shown as function of time and frequency at six streamwise stations, F=0.28, D=10%, B=1.0, Re=50,000; the solid white line is the leading edge of disturbance, and the dashed white line is the trailing edge

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Figure 22

Wavelet spectra computed at y locations of maximum u′ in time averaged profiles and shown as function of time and frequency at six streamwise stations, F=0.56, D=10%, B=0.75, Re=50,000; the solid white line is leading edge of disturbance, and the dashed line is trailing edge

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Figure 23

Cp profile for B=1, F=0.28, D=10%, Re=50,000

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Figure 24

U/Ue for B=1, F=0.28, D=10%, Re=50,000

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Figure 25

Q-criterion contours colored by axial velocity, B=1, F=0.28, D=10%, Re=50,000, at different times in the cycle

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