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Research Papers

Effects of Tip Gap Size on the Aerodynamic Performance of a Cavity-Winglet Tip in a Turbine Cascade

[+] Author and Article Information
Fangpan Zhong

College of Engineering,
Peking University,
Beijing 100871, China
e-mail: zhongfp@pku.edu.cn

Chao Zhou

State Key Laboratory for Turbulence and Complex Systems,
BIC-ESAT,
Collaborative Innovation Center of
Advanced Aero-Engine,
Peking University,
Beijing 100191, China
e-mail: czhou@pku.edu.cn

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received May 22, 2016; final manuscript received May 2, 2017; published online May 23, 2017. Assoc. Editor: Rolf Sondergaard.

J. Turbomach 139(10), 101009 (May 23, 2017) (9 pages) Paper No: TURBO-16-1106; doi: 10.1115/1.4036677 History: Received May 22, 2016; Revised May 02, 2017

The aerodynamic performance of a cavity-winglet tip is investigated in a high-pressure turbine cascade by experimental and numerical methods. The winglet tip has geometric features of a cavity and a suction side fore-part winglet. A cavity tip is studied as the baseline case. The aerodynamic performances of the two tips are investigated at three tip gaps of 0.8%, 1.7%, and 2.7% chord. At tip gaps of 1.7% and 2.7% chord, the loss near the blade tip is dominated by the tip leakage vortex (TLV) for both tips, and the winglet tip mainly reduces the loss generated by the tip leakage vortex. In the past, it was concerned that at a small tip gap, the winglet tip could introduce extra secondary loss and show little aerodynamic benefits. The winglet tip used in the current study is also found to be able to effectively reduce the loss at the smallest tip gap size of 0.8% chord. This is because at this small tip gap, the tip leakage vortex and the passage vortex (PV) appear simultaneously for the cavity tip. The winglet tip is able to reduce the pitchwise pressure gradient in the blade passage, which tends to suppress the formation of the passage vortex. The effects of the winglet tip on the flow physics and the loss mechanisms are explained in detail.

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Figures

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Fig. 1

Low-speed linear cascade of Peking University

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Fig. 2

Schematic of the cascade

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Fig. 3

Tip geometries: (a) cavity tip and (b) winglet tip

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Fig. 4

Computational domain and mesh of the cavity tip at τ = 1.7%C

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Fig. 5

Static pressure distribution around blade surface at a distance from blade tip of (a) 56% span and (b) 12% span

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Fig. 6

Cp0 distribution on the cascade exit plane, flat tip at τ = 1.7%C: (a) EXP and (b) CFD

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Fig. 7

Cp0 distribution of two tips on cascade exit plane, EXP: (a) cavity, 0.8%C, (b) cavity, 1.7%C, (c) cavity, 2.7%C, (d) winglet, 0.8%C, (e) winglet, 1.7%C, and (f) winglet, 2.7%C

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Fig. 8

Circumferential average Cp0 and β at τ = 2.7%C: (a) total pressure loss coefficient and (b) yaw angle

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Fig. 9

Circumferential average Cp0 and β at τ = 1.7%C: (a) total pressure loss coefficient and (b) yaw angle

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Fig. 10

Circumferential average Cp0 and β at τ = 0.8%C: (a) total pressure loss coefficient and (b) yaw angle

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Fig. 11

Constant-area mixing calculation

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Fig. 12

Mixed-out tip leakage loss coefficient of two tips at different tip clearances

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Fig. 13

Velocity vectors at tip gap exits of two tips, CFD: (a) τ = 0.8%C, (b) τ = 1.7%C, and (c) τ = 2.7%C

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Fig. 14

Flow angle difference between the two tips at tip gap exit, CFD

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Fig. 15

Relative reduction of tip leakage mass flow by the winglet tip, CFD

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Fig. 16

Near-tip flow streamlines of cavity tip and winglet tip at τ = 0.8%C, CFD: (a) cavity and (b) winglet

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Fig. 17

Cp0 distribution on the plane normal to the blade suction side at the trailing edge at τ = 0.8%C, CFD: (a) cavity and (b) winglet

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Fig. 18

Static pressure coefficient distribution on the endwall, CFD: (a) cavity, τ = 0.8%C, (b) winglet, τ = 0.8%C, (c) cavity, τ = 2.7%C, and (d) winglet, τ = 2.7%C

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