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Research Papers

Control of Tip Leakage in a High-Pressure Turbine Cascade Using Tip Blowing

[+] Author and Article Information
Ralph J. Volino

Fellow ASME
Mechanical Engineering Department,
United States Naval Academy,
Annapolis, MD 21402
e-mail: volino@usna.edu

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 27, 2016; final manuscript received November 6, 2016; published online February 7, 2017. Editor: Kenneth Hall.

J. Turbomach 139(6), 061008 (Feb 07, 2017) (12 pages) Paper No: TURBO-16-1176; doi: 10.1115/1.4035509 History: Received July 27, 2016; Revised November 06, 2016

Blowing from the tip of a turbine blade was studied experimentally to determine if total pressure loss could be reduced. Experiments were done with a linear cascade in a low-speed wind tunnel. Total pressure drop through the blade row and secondary velocity fields in the passage between two blades were measured. Cases were documented with various blowing hole configurations on flat and squealer tipped blades. Blowing normal to the tip was not helpful and in some cases increased losses. Blowing from the bottom of a squealer cavity provided little benefit. With a flat tip, blowing from holes located near and inclined toward the pressure side generally reduced total pressure drop by reducing the effect of the tip leakage vortex. Holes near the axial location of maximum loading were most helpful, while holes closer to the leading and trailing edges were not as effective. Higher jet velocity resulted in larger total pressure drop reduction. With a tip gap of 1.5% of axial chord, jets with a velocity 1.5 times the cascade inlet velocity had a significant effect. A total pressure drop reduction of the order 20% was possible using a jet mass flow of about 0.4% of the main flow. Jets were most effective with smaller tip gaps, as they were more able to counter the leakage flow.

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Figures

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Fig. 1

Schematic of linear cascade

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Fig. 2

Squealer tip: (a) top view showing squealer cavity and (b) bottom view showing internal cavity for jet supply air

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Fig. 3

Measurement planes for PIV and total pressure

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Fig. 4

Squealer tip with 11 inclined holes

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Fig. 5

Squealer tip with central rib and ten inclined holes

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Fig. 6

Area-averaged (0 < z/Cx < 1.1) total pressure coefficient normalized on B = 0 value for flat tip with seven 45 deg inclined holes of indicated diameters. Open symbols—uncontrolled passage and solid symbols—controlled passage. Note: All the figures for Re = 30,000, 30 deg inclined holes of d/Cx = 0.038, 0.015Cx tip gap unless otherwise noted.

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Fig. 7

Flat tip with seven inclined holes

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Fig. 8

Area-averaged (0 < z/Cx < 1.1) total pressure coefficient normalized on B = 0 value for flat tip with seven inclined holes of indicated angles; open symbols—uncontrolled passage and solid symbols—controlled passage

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Fig. 9

Area-averaged total pressure coefficient normalized on B = 0 value with blowing from indicated holes: (a) average over 0 < z/Cx < 1.1 and (b) average over 0 < z/Cx < 0.6

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Fig. 10

Pressure profiles on blades, blowing from holes 3 to 4; open symbols—midspan and solid symbols—0.32Cx from tip

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Fig. 11

Flat tip with nine inclined holes

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Fig. 12

Area-averaged (0 < z/Cx < 0.6) total pressure coefficient normalized on B = 0 value with blowing from indicated holes

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Fig. 13

ψ contours 0.1Cx downstream of trailing edges: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2. Note: All the figures here and below for blowing from holes 3 and 4 of Fig. 7 and Table 3.

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Fig. 14

Pitchwise-averaged ψ for contours of Fig. 13

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Fig. 15

ψ contours 0.7Cx downstream of trailing edges: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 16

Pitchwise-averaged ψ for contours of Fig. 15

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Fig. 17

Velocity vectors and λCx/Ui contours: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 18

Turbulence quantities in plane 1: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 19

Turbulence quantities in plane 2: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 20

ψ contours 0.1Cx downstream of trailing edges, Re = 60,000: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 21

ψ contours 0.7Cx downstream of trailing edges, Re = 60,000: (a) B = 0, (b) B = 1, (c) B = 1.5, and (d) B = 2

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Fig. 22

Pitchwise-averaged ψ for contours of Fig. 20

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Fig. 23

Pitchwise-averaged ψ for contours of Fig. 21

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Fig. 24

Area-averaged (0 < z/Cx < 0.6) total pressure coefficient normalized on B = 0 value at Re = 30,000 (solid symbols) and Re = 60,000 (open symbols)

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Fig. 25

ψ contours 0.1Cx downstream of trailing edges: (a) 0.01Cx gap, B = 0, (b) 0.01Cx gap, B = 1.5, (c) 0.02Cx gap, B = 0, and (d) 0.02Cx gap, B = 1.5

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Fig. 26

Area-averaged (0 < z/Cx < 0.6) total pressure coefficient normalized on B = 0 value for different tip gaps

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Fig. 27

Velocity vectors and λCx/Ui contours: (a) 0.01Cx gap, B = 0, (b) 0.01Cx gap, B = 1.5, (c) 0.02Cx gap, B = 0, and (d) 0.02Cx gap, B = 1.5

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Fig. 28

Tip leakage vortex strength as a function of tip gap size for cases with and without blowing in planes 1 and 2

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