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Research Papers

Effect of Unsteady Wakes on Boundary Layer Separation on a Very High Lift Low Pressure Turbine Airfoil

[+] Author and Article Information
Ralph J. Volino

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

J. Turbomach 134(1), 011011 (May 26, 2011) (16 pages) doi:10.1115/1.4003232 History: Received September 03, 2010; Revised October 23, 2010; Published May 26, 2011; Online May 26, 2011

Boundary layer separation has been studied on a very high lift, low pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Wakes were produced from moving rods upstream of the cascade. Flow coefficients were varied from 0.35 to 1.4 and wake spacing was varied from one to two blade spacings, resulting in dimensionless wake passing frequencies F=fLj-te/Uave (f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface of the airfoils, and Uave is the average freestream velocity) ranging from 0.14 to 0.56. 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 and downstream of the cascade. 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. In cases without wakes, the boundary layer separated and did not reattach. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. At lower frequencies the boundary layer separated between wakes. Background freestream turbulence had some effect on separation, but its role was secondary to the wake effect.

Copyright © 2012This material is declared a work of the US government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.
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References

Figures

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Figure 1

Schematic of linear cascade

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Figure 2

Velocity in wakes of wake generator rods and cascade wakes with low TI: (a) mean and (b) rms

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Figure 3

Velocity in wakes of wake generator rods and phase averaged velocity in wakes of cascade blades for low TI, Re=50,000 case with VGJ flow control (24): (a) mean and (b) rms

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Figure 4

Wavelet spectra of wake velocity: (a) cascade blades for low TI, Re=50,000 case with VGJ flow control (24) and (b) wake generator rods

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Figure 5

Pressure profiles for low TI, Re=25,000 cases: (a) Cp and (b) total pressure loss

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Figure 6

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=25,000, ζ=0.7, and 2Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 7

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=25,000, ζ=0.7, and 1.6Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 8

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=25,000, ζ=0.7, and 1Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 9

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=25,000, ζ=0.35, and 1.6Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 10

Time averaged velocity profiles at six streamwise stations for low TI, Re=25,000, and ζ=0.7 cases: top—mean and bottom—rms

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Figure 11

Phase averaged mean velocity profiles for low TI, Re=25,000, ζ=0.7, and 2Lϕ rod spacing; columns for six streamwise stations; rows for phases in wake cycle

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Figure 12

Phase averaged mean (rows 1 and 3) and rms streamwise fluctuating (rows 2 and 4) velocity for low TI, Re=25,000, and ζ=0.7: (a) 2Lϕ rod spacing and (b) 1.6Lϕ rod spacing

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Figure 13

Phase averaged momentum thickness for low TI, Re=25,000, and ζ=0.7: (a) 2Lϕ rod spacing and (b) 1.6Lϕ rod spacing; lines show leading edge (solid) and trailing edge (dashed-dotted) of wake, and trailing edge of the calm region (dashed)

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Figure 14

Pressure profiles for low TI and Re=50,000 cases: (a) Cp and (b) total pressure loss

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Figure 15

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=50,000, ζ=0.7, and 2Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 16

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=50,000, ζ=0.7, and 1.6Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 17

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for low TI, Re=50,000, ζ=0.7, and 1Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 18

Time averaged velocity profiles at six streamwise stations for low TI, Re=50,000, and ζ=0.7 cases: top—mean and bottom—rms

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Figure 19

Phase averaged mean velocity profiles for low TI, Re=50,000, ζ=0.7 cases, and 2Lϕ rod spacing; columns for six streamwise stations; rows for phases in wake cycle

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Figure 20

Phase averaged mean (rows 1 and 3) and rms streamwise fluctuating (rows 2 and 4) velocity for low TI and Re=50,000: (a) ζ=0.7,2Lϕ and (b) ζ=1.4,1.6Lϕ

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Figure 21

Phase averaged momentum thickness for low TI and Re=50,000: (a) ζ=0.7,2Lϕ and (b) ζ=1.4,1.6Lϕ

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Figure 22

Pressure profiles for high TI and Re=25,000 cases: (a) Cp and (b) total pressure loss

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Figure 23

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for high TI, Re=25,000, ζ=0.7, and 1.6Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 24

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for high TI, Re=25,000, ζ=0.7, and 1Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 25

Pressure profiles for high TI and Re=50,000 cases: (a) Cp and (b) total pressure loss spacing: (a) U/Ue and (b) u′/Ue

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Figure 26

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for high TI, Re=50,000, ζ=0.7, and 1.6Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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Figure 27

Time-space plot of phase averaged velocity 0.63Cx downstream of cascade for high TI, Re=50,000, ζ=0.7, and 1Lϕ rod spacing: (a) U/Ue and (b) u′/Ue

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